Vaccine 33 (2015) 4141–4145
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Vaccine journal homepage: www.elsevier.com/locate/vaccine
Serological response following re-vaccination with Salmonella typhi Vi-capsular polysaccharide vaccines in healthy adult travellers Louise Roggelin a,∗ , Christof D. Vinnemeier a , Johanna Fischer-Herr a , Brandi T. Johnson-Weaver b , Thierry Rolling a , Gerd D. Burchard a,c , Herman F. Staats b , Jakob P. Cramer a,c a
Section Tropical Medicine, 1. Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany Department of Pathology, Duke University Medical Center, Durham, NC, USA c Section Clinical Research and Epidemiology, Bernhard Nocht Institute of Tropical Medicine, Hamburg, Germany b
a r t i c l e
i n f o
Article history: Received 27 January 2015 Received in revised form 26 May 2015 Accepted 27 May 2015 Available online 2 July 2015 Keywords: Typhoid fever Vaccination Immunotolerance Hyporesponsiveness Vi antigen Polysaccharide
a b s t r a c t An injectable Vi-capsular polysaccharide vaccine against typhoid fever is available but vaccine-induced immunity tends to wane over time. The phenomenon of immunotolerance or hyporesponsiveness has earlier been described for polysaccharide vaccines such as pneumococcal capsular polysaccharide vaccine and some publications also suggest a possible immunotolerance after revaccination with Vi-capsular polysaccharide vaccines. In this study, post-immunisation antibody concentrations in adult travellers first vaccinated with a Salmonella typhi Vi-capsular polysaccharide vaccine (primary vaccination group) were compared with those having received one or more vaccinations previously (multiple vaccinations group). Vaccines administered were Typherix® (GlaxoSmithKline), Typhim Vi® (Sanofi Pasteur MSD) or Hepatyrix® (GlaxoSmithKline). Blood samples were obtained prior to vaccination (day 0) and on day 28 (−1/+14) after vaccination. Serum Vi-Antigen IgG concentrations were measured by ELISA. Of the 85 subjects included in the per protocol data set, 45 (53%) belonged to the multiple vaccinations group. In both groups, geometric mean antibody concentrations (GMCs) were significantly higher after vaccination than before vaccination. Pre-vaccination GMCs were lower in the primary vaccination group than in the multiple vaccinations group (3.40 g/ml versus 6.13 g/ml, P = 0.005), while there was no significant difference in the post vaccination GMCs between groups (11.34 g/ml versus 14.58 g/ml, P = 0.4). In the multiple vaccinations group, vaccination was performed 18 to 57 months after the last vaccination (median 38 months) and there was a negative correlation between time since last vaccination and antibody concentration on day 0. In conclusion, we were not able to demonstrate a relevant immunotolerance after multiple versus primary vaccination with S. typhi Vi-capsular polysaccharide vaccines. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction In countries with limited food hygiene and sanitation infrastructure, typhoid fever still presents a major burden of disease and poses a risk to travellers to these regions [1,2]. Besides an
∗ Corresponding author. Present address: Section Tropical Medicine, 1. Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. Tel.: +0049 17616408753. E-mail addresses: [email protected] (L. Roggelin), [email protected] (C.D. Vinnemeier), [email protected] (J. Fischer-Herr), [email protected] (B.T. Johnson-Weaver), [email protected] (T. Rolling), burchard@ifi-medizin.de (G.D. Burchard), [email protected] (H.F. Staats), [email protected] (J.P. Cramer). http://dx.doi.org/10.1016/j.vaccine.2015.05.080 0264-410X/© 2015 Elsevier Ltd. All rights reserved.
oral Salmonella typhi Ty21a vaccine, injectable polysaccharide (PS) vaccines containing S. typhi Vi-capsular antigen are available. Protective efficacy of typhoid fever vaccines is not optimal and immunity tends to wane over time. Large trials on the protective efficacy of the Vi-capsular polysaccharide vaccines were performed in areas where S. typhi is endemic [3–5]. A trial in Nepal demonstrated an efficacy of 72% of the Vi-capsular polysaccharide vaccines in preventing typhoid fever within 17 months of follow-up [4]. In another trial in South Africa, protective efficacy after 3 years was calculated as 55% while 64% of the vaccinees had an antibody concentration over 1 g/ml at that time [3]. In non-endemic regions, protective efficacy can only be estimated indirectly by measuring vaccine-specific antibody
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concentrations. Estimated protective concentrations vary, probably due to different serologic assays and antibody standards [3,5,6]. Trials in non-endemic regions demonstrated a rapid decline of antibody concentration during the three years following vaccination [7–9]. A trial in the USA demonstrated a progressive decrease in the proportion of vaccinees with concentrations of ≥1 g/ml from 87% after one month to only 35% after 3 years post-vaccination. Thus, in many industrialized countries it is recommended to revaccinate against typhoid fever after two or three years if extended protection is needed [10–12]. The phenomenon of immunotolerance, reflecting the overall lower increase in antibody concentration after re-vaccination compared to primary vaccination has been described for polysaccharide vaccines such as pneumococcal capsular polysaccharide vaccine or meningococcal serogroup C (MenC) vaccines [13,14]. Several immune mechanisms, including the depletion of the B-memory pool could be possible explanations for this phenomenon [14]. Recent findings also suggest a possible immunotolerance after re-vaccination with Vi-capsular S. typhi polysaccharide vaccines but results are controversial: Overbosch et al. observed a lower seroprotection and seroconversion after Vi-capsular re-vaccination than after the initial vaccination 3 years earlier [9]. Keitel et al., on the other hand, showed comparable results regarding antibody concentrations one month after primary immunization versus after re-immunization administered 27 or 34 month after primary immunization [7]. In the present study, anti Vi-capsular antibody concentrations have been assessed in travellers receiving their first vaccination (primary vaccination group) versus those having received one or more previous vaccinations (multiple vaccination group) with a Vicapsular polysaccharide vaccine.
2. Materials and methods The study was conducted at the pre-travel clinic of the Section Tropical Medicine of the University Medical Center HamburgEppendorf, Germany, between January 2012 and June 2013. All subjects had sought pre-travel consultation and vaccination against typhoid fever was indicated following recommendations of the German Society for Tropical Medicine and International Health [10]. In brief, travellers to tropical/subtropical areas with limited hygiene and sanitation conditions staying more than 4 weeks (Indian subcontinent: any travel duration) were offered typhoid fever vaccination as well as all travellers inquiring maximum protection. Subjects over 18 years of age with (multiple vaccinations group) or without (primary vaccination group) previous parental typhoid fever vaccination were included after providing written informed consent. Exclusion criteria included concurrent febrile illness, severe chronic disease, relevant allergies, illness/medication associated with immunosuppression and past history of typhoid fever. Subjects with previous vaccination must have received their last vaccination with S. typhi Vi-capsular polysaccharide vaccine not more than 5 years ago. After inclusion, subjects received a single dose of typhoid fever vaccination composed of purified Vi polysaccharide into the right or left deltoid muscle. Vaccines administered were Typherix® (GlaxoSmithKline), Typhim Vi® (Sanofi Pasteur MSD) or Hepatyrix® (GlaxoSmithKline). Each dose of monovalent typhoid vaccine (Typherix® and Typhin Vi® ) consisted of 0.025 mg S. typhi Vi-polysaccharide antigen, Hepatyrix® additionally contained 1440 ELISA units of inactivated hepatitis A virus. Blood samples were obtained via venipuncture on day 0 prior to vaccination and on day 28 (−1/+14) after vaccination. Sera were prepared immediately from all blood samples and stored at −20 ◦ C until shipment for serologic analyses. Laboratory
personnel performing serum antibody analyses were blinded to study group allocation of respective serum samples. Serum Viantigen IgG concentrations were measured by an in-house ELISA as described before [15]. Vi-polysaccharide (Typhim) at a concentration of 1 g/ml was used to coat plates and incubated at room temperature for 3 h. Plates were blocked with carbonate/bicarbonate buffer and non-fat dry milk at 4 ◦ C overnight. Vi-standard and experimental samples were diluted 2-fold beginning at a starting dilution of 1:50. Samples were added to ELISA plates and incubated at 37 ◦ C for 1 h. A Vi-standard curve was performed on each ELISA plate using a pooled serum sample from study participants with elevated Vi-specific IgG responses. The pooled serum sample had an anti-Vi IgG concentration of 13.60 g/ml as determined by comparison to the FDA anti-Vi IgG reference sample R1, 2011 [6]. Plates were washed and a goat-anti human IgG-AP secondary antibody was added to plates at a dilution of 1:10,000. After incubating for 1 h at 37 ◦ C, plates were washed and AttoPhos® (alkaline phosphatase fluorescent) substrate was added allowed to incubate at room temperature for 1 h. The Vi-standard curve on each plate was used to calculate the anti-Vi IgG g/ml concentration in each experimental sample assayed on the same plate. The study was approved by the ethics committee of the Physicians’ Chamber Hamburg, Germany. Statistics software SPSS 17.0 was used to analyse data. A P-value 4.3 g/ml prior to vaccination, 70% of the primary vaccination group and 78% of the multiple vaccinations group had an antibody concentration of >4.3 g/ml after vaccination. As expected, pre-vaccination GMC was lower in the primary vaccination group than in the multiple vaccination group, while there was no significant difference in the post-vaccination GMC between groups. Furthermore, there were no differences regarding the relative (fold) nor absolute increase in GMC nor the proportion of ≥fourfold antibody concentration increase (Table 3). Within the multiple vaccinations group, re-vaccination was performed after a median of 38 months after their last vaccination (range 18–57). Time after previous vaccination was stratified into two time frames: 19 (42%) subjects were re-vaccinated ≤36 months and 26 (58%) subjects were re-vaccinated >36–60 months after their previous vaccination. There was no significant difference between GMC on day 0 or day 28 between both groups (day 0: 7.10 g/ml vs. 5.42 g/ml, P = 0.314; day 28: 10.62 g/ml vs. 17.46 g/ml, P = 0.269). Fig. 1 shows the correlation between anti Vi-capsular IgG concentration and time since last vaccination in
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months before (Fig. 1a) and after (Fig. 1b) the current vaccination. Before re-vaccination, there is a negative association between time after previous vaccination and anti Vi-capsular IgG concentration. The time since previous vaccination had no influence on the post re-vaccination antibody concentration (Fig. 1b). Next, the influence of the number of previous vaccinations on post-vaccination antibody concentrations was analysed in the multiple vaccinations group. Thirty-six had been vaccinated once and nine had been vaccinated at least twice before re-vaccination (six had been vaccinated twice, two had been vaccinated three times and one had been vaccinated four times before). Table 4 shows pre- and post-vaccination GMC stratified according to the number of previous Vi-capsular polysaccharide vaccinations. The subgroup of those who had been pre-vaccinated once shows the highest post-vaccination GMC compared to those who had been vaccinated twice before or received their primary vaccination (Table 4). 4. Discussion In the present study we investigated a possible effect of immunotolerance or hyporesponsiveness after multiple vaccinations with the parenteral S. typhi Vi-capsular polysaccharide vaccine. Post-vaccination antibody concentrations were comparable between groups of primary versus multiple vaccinations. Prevaccination antibody concentrations were numerically highest in those who received two previous vaccination and post-vaccination antibody concentrations were numerically highest in those who received one previous vaccinations. However the latter difference did not achieve statistical significance. Pre-vaccination antibody concentrations were higher in previously vaccinated compared to vaccine immune-naïve subjects. However the relative increase of post-vaccination concentrations was numerically higher in the primary vaccination group compared to the multiple vaccinations group while absolute post-vaccination concentrations were comparable between groups. Therefore, these observations do not entirely exclude an immunotolerance phenomenon after multiple Vi-capsular vaccinations as one may expect a relatively higher absolute rise in antibody concentration, i.e. a booster response, after multiple vaccinations compared to primary vaccination. There were some sociodemographic differences between groups in that within the multiple vaccinations group reported more frequently previous travel to areas with risk of S. typhi transmission. Yet, it appears unlikely that this may have a relevant influence on the findings in our study sample for example by
Fig. 1. Correlation between pre-vaccination antibody concentration day 0 (a) as well as post-vaccination antibody concentration on day 28 (b) and time since last Salmonella typhi Vi-capsular polysaccharide vaccine measured in month. (a) y = 12,467−0.166x R2 = 0.093 P = 0.041. (b) y = 10,194−0.144x R2 = 0.003 P = 0.712.
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Table 3 Pre- and post-vaccination antibody response to S. typhi Vi-capsular polysaccharide vaccination. Day 0
Primary vaccination group Multiple vaccination group P-value2 primary vaccination/multiple vaccination
Day 28 GMC (g/ml)
% > 4.3 g/ml
3.40 (2.52–4.28) 25 (10/40)
11.34 (7.20–15.49)
70 (28/40)
6.13 (4.50–7.76) 49 (22/45)
14.58 (8.49–20.66)
78 (35/45)
n
GMC (g/ml)
40 (47%) 45 (53%)
% > 4.3 g/ml
Mean foldconcentration increase (day 0/day 28)
% ≥ fourfold concentration increase
4.3 g/ml
3.40 (2.52–4.28)
25 (10/40)
11.34 (7.20–15.49)
70 (28/40)
4.3 g/ml
n
0.007
0.254 8.49 (3.79–13.19) 0.525
P-value (day 0/day 28)
Mean foldconcentration increase (day 28/day 0)
0.106
GMC = geometric mean Vi antibody concentration, (95% CI). * Compared with primary vaccinations group.
natural immunization via infections. As shown in an analysis on ill-returning travellers within the global network GeoSentinel, S. typhi—related infections occur very rarely even in high risk travellers [16]. Among 37542 ill-returning travellers analysed for potentially vaccine-preventable diseases within the same network, S. typhi was confirmed in 160 cases [17]. In the multiple vaccinations group, there is a correlation between time since last vaccination and pre-vaccination antibody concentration reflecting a waning immunity after Vi-capsular vaccination which is in line with previously published findings [7–9]. For post-vaccination antibody concentrations – on the other hand – there is no significant correlation with time since last vaccination. This finding indicates that the time since last vaccination does not influence post-vaccination antibody concentrations after multiple vaccinations in a relevant way. Immunotolerance after revaccination describes the inability to mount an immune response higher to – or at least comparable to – the immune response after first vaccination. Most likely this effect is due to the fact that unconjugated polysaccharides induce T-cell independent immune responses. Thereby polysaccharides stimulate but not replenish immune memory cell leading to a depletion of the B-memory pool [14,18]. All in all, although some effect related to immunotolerance cannot be excluded from our data, our data do not support a relevant immunotolerance after multiple Vi-polysaccharide vaccinations as described previously [9] but is in line with data published earlier [7]. As many travellers tend to travel to tropical or subtropical regions more than once during their life, extended protection is often needed or requested. Immunotolerance after multiple parental Vi-capsular polysaccharide vaccines could lead to
an increased risk of infection upon exposure during travel in particular when departing from countries where oral whole cell/life-attenuated vaccines based on the Ty21a-strain are not available. Our data, however, does not argue against multiple subsequent vaccinations with the parental S. typhi Vi-capsular polysaccharide vaccines, especially as earlier studies also demonstrated a good tolerance of the parental vaccination [19]. Another option is to alternately vaccinate with the oral S. typhi Ty21a vaccine if available which may also provide immunoprotection against S. paratyphi [20,21] and offers a good alternative for subsequent vaccination after previous parental polysaccharide vaccine(s). According to the manufacturers’ instructions, re-vaccination with the oral/parenteral vaccines are recommended after 5/3 years, respectively [22–24]. A limitation of the study was the rather small sample size. To estimate the serological response following multiple re-vaccinations with S. typhi Vi-capsular polysaccharide vaccines in travellers further studies with larger samples sizes are desirable. Absolute antibody concentration are difficult to compare to other data published earlier [7,9], probably due to different inhouse tests and standard curves. We therefore calculated our data by comparison to an FDA reference sample to allow comparison to some data published earlier [5,6] and further studies to come. Yet, the internal validity of our study is not affected and findings are, therefore, appropriate to answer the respective research question of the present study. 5. Conclusion In conclusion, we were not able to demonstrate a relevant immunotolerance after multiple versus primary vaccination with S. typhi Vi-capsular polysaccharide vaccines.
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Contributors LR, CDV, JFH and TR participated in patient recruitment and data collection. LR performed the statistical analyses and drafted the manuscript. JPC conceived of the study and participated in its design and coordination and helped to draft the manuscript. CDV, JFH, GDB significantly contributed to the protocol development and/or study implementation. All authors read and revised the manuscript and approved the final version. The analysis forms part of the doctoral thesis of LR. Conflict of interests statements CDV, JFH, GDB and JPC participated in industry-sponsored clinical trials that included typhoid fever vaccines. JPC has received consulting honoraries from industrial companies producing typhoid fever vaccines. LR and TR have no conflict of interest. Acknowledgements The authors would like to thank the entire staff at the Bernhard Nocht Center for Clinical Trials (www.bncct.de), in particular Mrs. Sabine Eberhardt and Mrs. Anja Wentzin, for their enduring and valuable support. References [1] Crump JA, Mintz ED. Global trends in typhoid and paratyphoid fever. Clin Infect Dis 2010;50:241–6. [2] Whitaker JA, Franco-Paredes C, del Rio C, Edupuganti S. Rethinking typhoid fever vaccines: implications for travelers and people living in highly endemic areas. J Travel Med 2009;16:46–52. [3] Klugman KP, Koornhof HJ, Robbins JB, Le Cam NN. Immunogenicity, efficacy and serological correlate of protection of Salmonella typhi Vi capsular polysaccharide vaccine three years after immunization. Vaccine 1996;14:435–8. [4] Acharya IL, Lowe CU, Thapa R, Gurubacharya VL, Shrestha MB, Cadoz M, et al. Prevention of typhoid fever in Nepal with the Vi capsular polysaccharide of Salmonella typhi. A preliminary report. N Engl J Med 1987;317:1101–4. [5] Lin FY, Ho VA, Khiem HB, Trach DD, Bay PV, Thanh TC, et al. The efficacy of a Salmonella typhi Vi conjugate vaccine in two-to-five-year-old children. N Engl J Med 2001;344:1263–9. [6] Szu SC, Hunt S, Xie G, Robbins JB, Schneerson R, Gupta RK, et al. A human IgG anti-Vi reference for Salmonella typhi with weight-based antibody units assigned. Vaccine 2013;31:1970–4.
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[7] Keitel WA, Bond NL, Zahradnik JM, Cramton TA, Robbins JB. Clinical and serological responses following primary and booster immunization with Salmonella typhi Vi capsular polysaccharide vaccines. Vaccine 1994;12:195–9. [8] Froeschle JE, Decker MD. Duration of Vi antibodies in participants vaccinated with Typhim Vi (Typhoid Vi polysaccharide vaccine) in an area not endemic for typhoid fever. Vaccine 2010;28:1451–3. [9] Overbosch D, Peyron F, Picot N, Varichon JP, Dumas R, Chambonneau L. et al Combined typhoid fever and hepatitis A vaccine: comparison of immunogenicity and safety to concomitant monovalent vaccine over 3 years. J Trav Med 2005;12:319–26. [10] DTG. Typhus; 2006. Available from http://www.dtg.org/typhus.html (accessed 2013 06 Dec). [11] HPA. Typhoid—health advise for travelers; 12 Dec, 2011. Available from https://www.gov.uk/government/publications/typhoid-health-advice-fortravellers (accessed 2015 14 Apr). [12] CDC. Typhoid fever; 2013. Available from http://www.cdc.gov/nczved/ divisions/dfbmd/diseases/typhoid fever/ (accessed 2013 06 Dec). [13] Assaad U, El-Masri I, Porhomayon J, El-Solh AA. Pneumonia immunization in older adults: review of vaccine effectiveness and strategies. Clin Interv Aging 2012;7:453–61. [14] Poolman J, Borrow R. Hyporesponsiveness and its clinical implications after vaccination with polysaccharide or glycoconjugate vaccines. Expert Rev Vaccines 2011;10:307–22. [15] Staats HF, Kirwan SM, Whisnant CC, Stephenson JL, Wagener DK, Majumder PP. Development of a bead immunoassay to measure Vi polysaccharide-specific serum IgG after vaccination with the Salmonella enterica serovar Typhi Vi polysaccharide. Clin Vaccine Immunol 2010;17:412–9. [16] Leder K, Torresi J, Libman MD, Cramer JP, Castelli F, Schlagenhauf P, et al. GeoSentinel surveillance of illness in returned travelers, 2007–2011. Ann Intern Med 2013;158(Mar):456–68. [17] Boggild AK, Castelli F, Gautret P, Torresi J, von Sonnenburg F, Barnett ED, et al. Vaccine preventable diseases in returned international travelers: results from the GeoSentinel Surveillance Network. Vaccine 2010;28:7389–95. [18] Granoff DM, Pollard AJ. Reconsideration of the use of meningococcal polysaccharide vaccine. Pediatr Infect Dis J 2007;26:716–22. [19] Anwar E, Goldberg E, Fraser A, Acosta CJ, Paul M, Leibovici L. Vaccines for preventing typhoid fever. Cochrane Database Syst Rev 2014;1:CD001261. [20] Pakkanen SH, Kantele JM, Kantele A. Cross-reactive gut-directed immune response against Salmonella enterica serovar Paratyphi A and B in typhoid fever and after oral Ty21a typhoid vaccination. Vaccine 2012;30(Sep):6047–53. [21] Pakkanen SH, Kantele JM, Kantele A. Cross-reactive gut-directed immune response against Salmonella enterica serovar Paratyphi A and B in typhoid fever and after oral Ty21a typhoid vaccination. Vaccine 2014;30:6047–53. [22] GlaxoSmithKline Inc. Typherix—product monograph; 2014. Available from http://www.gsk.ca/english/docs-pdf/product-monographs/Typherix.pdf (accessed 2014 Nov 06). [23] FDA. Vivotif package insert USA; 2013. Available from http://www.fda.gov/ downloads/BiologicsBloodVaccines/Vaccines/ApprovedProducts/UCM142807. pdf (accessed 2014 Nov 06). [24] Arzneimittelkompendium der Schweiz, Vivotif Package Insert Switzerland, 2015. Available from www.compendium.ch/mpro/mnr/26290/html/de (accessed 2015 Apr 14).
Contents lists available at ScienceDirect
Vaccine journal homepage: www.elsevier.com/locate/vaccine
Serological response following re-vaccination with Salmonella typhi Vi-capsular polysaccharide vaccines in healthy adult travellers Louise Roggelin a,∗ , Christof D. Vinnemeier a , Johanna Fischer-Herr a , Brandi T. Johnson-Weaver b , Thierry Rolling a , Gerd D. Burchard a,c , Herman F. Staats b , Jakob P. Cramer a,c a
Section Tropical Medicine, 1. Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany Department of Pathology, Duke University Medical Center, Durham, NC, USA c Section Clinical Research and Epidemiology, Bernhard Nocht Institute of Tropical Medicine, Hamburg, Germany b
a r t i c l e
i n f o
Article history: Received 27 January 2015 Received in revised form 26 May 2015 Accepted 27 May 2015 Available online 2 July 2015 Keywords: Typhoid fever Vaccination Immunotolerance Hyporesponsiveness Vi antigen Polysaccharide
a b s t r a c t An injectable Vi-capsular polysaccharide vaccine against typhoid fever is available but vaccine-induced immunity tends to wane over time. The phenomenon of immunotolerance or hyporesponsiveness has earlier been described for polysaccharide vaccines such as pneumococcal capsular polysaccharide vaccine and some publications also suggest a possible immunotolerance after revaccination with Vi-capsular polysaccharide vaccines. In this study, post-immunisation antibody concentrations in adult travellers first vaccinated with a Salmonella typhi Vi-capsular polysaccharide vaccine (primary vaccination group) were compared with those having received one or more vaccinations previously (multiple vaccinations group). Vaccines administered were Typherix® (GlaxoSmithKline), Typhim Vi® (Sanofi Pasteur MSD) or Hepatyrix® (GlaxoSmithKline). Blood samples were obtained prior to vaccination (day 0) and on day 28 (−1/+14) after vaccination. Serum Vi-Antigen IgG concentrations were measured by ELISA. Of the 85 subjects included in the per protocol data set, 45 (53%) belonged to the multiple vaccinations group. In both groups, geometric mean antibody concentrations (GMCs) were significantly higher after vaccination than before vaccination. Pre-vaccination GMCs were lower in the primary vaccination group than in the multiple vaccinations group (3.40 g/ml versus 6.13 g/ml, P = 0.005), while there was no significant difference in the post vaccination GMCs between groups (11.34 g/ml versus 14.58 g/ml, P = 0.4). In the multiple vaccinations group, vaccination was performed 18 to 57 months after the last vaccination (median 38 months) and there was a negative correlation between time since last vaccination and antibody concentration on day 0. In conclusion, we were not able to demonstrate a relevant immunotolerance after multiple versus primary vaccination with S. typhi Vi-capsular polysaccharide vaccines. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction In countries with limited food hygiene and sanitation infrastructure, typhoid fever still presents a major burden of disease and poses a risk to travellers to these regions [1,2]. Besides an
∗ Corresponding author. Present address: Section Tropical Medicine, 1. Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. Tel.: +0049 17616408753. E-mail addresses: [email protected] (L. Roggelin), [email protected] (C.D. Vinnemeier), [email protected] (J. Fischer-Herr), [email protected] (B.T. Johnson-Weaver), [email protected] (T. Rolling), burchard@ifi-medizin.de (G.D. Burchard), [email protected] (H.F. Staats), [email protected] (J.P. Cramer). http://dx.doi.org/10.1016/j.vaccine.2015.05.080 0264-410X/© 2015 Elsevier Ltd. All rights reserved.
oral Salmonella typhi Ty21a vaccine, injectable polysaccharide (PS) vaccines containing S. typhi Vi-capsular antigen are available. Protective efficacy of typhoid fever vaccines is not optimal and immunity tends to wane over time. Large trials on the protective efficacy of the Vi-capsular polysaccharide vaccines were performed in areas where S. typhi is endemic [3–5]. A trial in Nepal demonstrated an efficacy of 72% of the Vi-capsular polysaccharide vaccines in preventing typhoid fever within 17 months of follow-up [4]. In another trial in South Africa, protective efficacy after 3 years was calculated as 55% while 64% of the vaccinees had an antibody concentration over 1 g/ml at that time [3]. In non-endemic regions, protective efficacy can only be estimated indirectly by measuring vaccine-specific antibody
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concentrations. Estimated protective concentrations vary, probably due to different serologic assays and antibody standards [3,5,6]. Trials in non-endemic regions demonstrated a rapid decline of antibody concentration during the three years following vaccination [7–9]. A trial in the USA demonstrated a progressive decrease in the proportion of vaccinees with concentrations of ≥1 g/ml from 87% after one month to only 35% after 3 years post-vaccination. Thus, in many industrialized countries it is recommended to revaccinate against typhoid fever after two or three years if extended protection is needed [10–12]. The phenomenon of immunotolerance, reflecting the overall lower increase in antibody concentration after re-vaccination compared to primary vaccination has been described for polysaccharide vaccines such as pneumococcal capsular polysaccharide vaccine or meningococcal serogroup C (MenC) vaccines [13,14]. Several immune mechanisms, including the depletion of the B-memory pool could be possible explanations for this phenomenon [14]. Recent findings also suggest a possible immunotolerance after re-vaccination with Vi-capsular S. typhi polysaccharide vaccines but results are controversial: Overbosch et al. observed a lower seroprotection and seroconversion after Vi-capsular re-vaccination than after the initial vaccination 3 years earlier [9]. Keitel et al., on the other hand, showed comparable results regarding antibody concentrations one month after primary immunization versus after re-immunization administered 27 or 34 month after primary immunization [7]. In the present study, anti Vi-capsular antibody concentrations have been assessed in travellers receiving their first vaccination (primary vaccination group) versus those having received one or more previous vaccinations (multiple vaccination group) with a Vicapsular polysaccharide vaccine.
2. Materials and methods The study was conducted at the pre-travel clinic of the Section Tropical Medicine of the University Medical Center HamburgEppendorf, Germany, between January 2012 and June 2013. All subjects had sought pre-travel consultation and vaccination against typhoid fever was indicated following recommendations of the German Society for Tropical Medicine and International Health [10]. In brief, travellers to tropical/subtropical areas with limited hygiene and sanitation conditions staying more than 4 weeks (Indian subcontinent: any travel duration) were offered typhoid fever vaccination as well as all travellers inquiring maximum protection. Subjects over 18 years of age with (multiple vaccinations group) or without (primary vaccination group) previous parental typhoid fever vaccination were included after providing written informed consent. Exclusion criteria included concurrent febrile illness, severe chronic disease, relevant allergies, illness/medication associated with immunosuppression and past history of typhoid fever. Subjects with previous vaccination must have received their last vaccination with S. typhi Vi-capsular polysaccharide vaccine not more than 5 years ago. After inclusion, subjects received a single dose of typhoid fever vaccination composed of purified Vi polysaccharide into the right or left deltoid muscle. Vaccines administered were Typherix® (GlaxoSmithKline), Typhim Vi® (Sanofi Pasteur MSD) or Hepatyrix® (GlaxoSmithKline). Each dose of monovalent typhoid vaccine (Typherix® and Typhin Vi® ) consisted of 0.025 mg S. typhi Vi-polysaccharide antigen, Hepatyrix® additionally contained 1440 ELISA units of inactivated hepatitis A virus. Blood samples were obtained via venipuncture on day 0 prior to vaccination and on day 28 (−1/+14) after vaccination. Sera were prepared immediately from all blood samples and stored at −20 ◦ C until shipment for serologic analyses. Laboratory
personnel performing serum antibody analyses were blinded to study group allocation of respective serum samples. Serum Viantigen IgG concentrations were measured by an in-house ELISA as described before [15]. Vi-polysaccharide (Typhim) at a concentration of 1 g/ml was used to coat plates and incubated at room temperature for 3 h. Plates were blocked with carbonate/bicarbonate buffer and non-fat dry milk at 4 ◦ C overnight. Vi-standard and experimental samples were diluted 2-fold beginning at a starting dilution of 1:50. Samples were added to ELISA plates and incubated at 37 ◦ C for 1 h. A Vi-standard curve was performed on each ELISA plate using a pooled serum sample from study participants with elevated Vi-specific IgG responses. The pooled serum sample had an anti-Vi IgG concentration of 13.60 g/ml as determined by comparison to the FDA anti-Vi IgG reference sample R1, 2011 [6]. Plates were washed and a goat-anti human IgG-AP secondary antibody was added to plates at a dilution of 1:10,000. After incubating for 1 h at 37 ◦ C, plates were washed and AttoPhos® (alkaline phosphatase fluorescent) substrate was added allowed to incubate at room temperature for 1 h. The Vi-standard curve on each plate was used to calculate the anti-Vi IgG g/ml concentration in each experimental sample assayed on the same plate. The study was approved by the ethics committee of the Physicians’ Chamber Hamburg, Germany. Statistics software SPSS 17.0 was used to analyse data. A P-value 4.3 g/ml prior to vaccination, 70% of the primary vaccination group and 78% of the multiple vaccinations group had an antibody concentration of >4.3 g/ml after vaccination. As expected, pre-vaccination GMC was lower in the primary vaccination group than in the multiple vaccination group, while there was no significant difference in the post-vaccination GMC between groups. Furthermore, there were no differences regarding the relative (fold) nor absolute increase in GMC nor the proportion of ≥fourfold antibody concentration increase (Table 3). Within the multiple vaccinations group, re-vaccination was performed after a median of 38 months after their last vaccination (range 18–57). Time after previous vaccination was stratified into two time frames: 19 (42%) subjects were re-vaccinated ≤36 months and 26 (58%) subjects were re-vaccinated >36–60 months after their previous vaccination. There was no significant difference between GMC on day 0 or day 28 between both groups (day 0: 7.10 g/ml vs. 5.42 g/ml, P = 0.314; day 28: 10.62 g/ml vs. 17.46 g/ml, P = 0.269). Fig. 1 shows the correlation between anti Vi-capsular IgG concentration and time since last vaccination in
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months before (Fig. 1a) and after (Fig. 1b) the current vaccination. Before re-vaccination, there is a negative association between time after previous vaccination and anti Vi-capsular IgG concentration. The time since previous vaccination had no influence on the post re-vaccination antibody concentration (Fig. 1b). Next, the influence of the number of previous vaccinations on post-vaccination antibody concentrations was analysed in the multiple vaccinations group. Thirty-six had been vaccinated once and nine had been vaccinated at least twice before re-vaccination (six had been vaccinated twice, two had been vaccinated three times and one had been vaccinated four times before). Table 4 shows pre- and post-vaccination GMC stratified according to the number of previous Vi-capsular polysaccharide vaccinations. The subgroup of those who had been pre-vaccinated once shows the highest post-vaccination GMC compared to those who had been vaccinated twice before or received their primary vaccination (Table 4). 4. Discussion In the present study we investigated a possible effect of immunotolerance or hyporesponsiveness after multiple vaccinations with the parenteral S. typhi Vi-capsular polysaccharide vaccine. Post-vaccination antibody concentrations were comparable between groups of primary versus multiple vaccinations. Prevaccination antibody concentrations were numerically highest in those who received two previous vaccination and post-vaccination antibody concentrations were numerically highest in those who received one previous vaccinations. However the latter difference did not achieve statistical significance. Pre-vaccination antibody concentrations were higher in previously vaccinated compared to vaccine immune-naïve subjects. However the relative increase of post-vaccination concentrations was numerically higher in the primary vaccination group compared to the multiple vaccinations group while absolute post-vaccination concentrations were comparable between groups. Therefore, these observations do not entirely exclude an immunotolerance phenomenon after multiple Vi-capsular vaccinations as one may expect a relatively higher absolute rise in antibody concentration, i.e. a booster response, after multiple vaccinations compared to primary vaccination. There were some sociodemographic differences between groups in that within the multiple vaccinations group reported more frequently previous travel to areas with risk of S. typhi transmission. Yet, it appears unlikely that this may have a relevant influence on the findings in our study sample for example by
Fig. 1. Correlation between pre-vaccination antibody concentration day 0 (a) as well as post-vaccination antibody concentration on day 28 (b) and time since last Salmonella typhi Vi-capsular polysaccharide vaccine measured in month. (a) y = 12,467−0.166x R2 = 0.093 P = 0.041. (b) y = 10,194−0.144x R2 = 0.003 P = 0.712.
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Table 3 Pre- and post-vaccination antibody response to S. typhi Vi-capsular polysaccharide vaccination. Day 0
Primary vaccination group Multiple vaccination group P-value2 primary vaccination/multiple vaccination
Day 28 GMC (g/ml)
% > 4.3 g/ml
3.40 (2.52–4.28) 25 (10/40)
11.34 (7.20–15.49)
70 (28/40)
6.13 (4.50–7.76) 49 (22/45)
14.58 (8.49–20.66)
78 (35/45)
n
GMC (g/ml)
40 (47%) 45 (53%)
% > 4.3 g/ml
Mean foldconcentration increase (day 0/day 28)
% ≥ fourfold concentration increase
4.3 g/ml
3.40 (2.52–4.28)
25 (10/40)
11.34 (7.20–15.49)
70 (28/40)
4.3 g/ml
n
0.007
0.254 8.49 (3.79–13.19) 0.525
P-value (day 0/day 28)
Mean foldconcentration increase (day 28/day 0)
0.106
GMC = geometric mean Vi antibody concentration, (95% CI). * Compared with primary vaccinations group.
natural immunization via infections. As shown in an analysis on ill-returning travellers within the global network GeoSentinel, S. typhi—related infections occur very rarely even in high risk travellers [16]. Among 37542 ill-returning travellers analysed for potentially vaccine-preventable diseases within the same network, S. typhi was confirmed in 160 cases [17]. In the multiple vaccinations group, there is a correlation between time since last vaccination and pre-vaccination antibody concentration reflecting a waning immunity after Vi-capsular vaccination which is in line with previously published findings [7–9]. For post-vaccination antibody concentrations – on the other hand – there is no significant correlation with time since last vaccination. This finding indicates that the time since last vaccination does not influence post-vaccination antibody concentrations after multiple vaccinations in a relevant way. Immunotolerance after revaccination describes the inability to mount an immune response higher to – or at least comparable to – the immune response after first vaccination. Most likely this effect is due to the fact that unconjugated polysaccharides induce T-cell independent immune responses. Thereby polysaccharides stimulate but not replenish immune memory cell leading to a depletion of the B-memory pool [14,18]. All in all, although some effect related to immunotolerance cannot be excluded from our data, our data do not support a relevant immunotolerance after multiple Vi-polysaccharide vaccinations as described previously [9] but is in line with data published earlier [7]. As many travellers tend to travel to tropical or subtropical regions more than once during their life, extended protection is often needed or requested. Immunotolerance after multiple parental Vi-capsular polysaccharide vaccines could lead to
an increased risk of infection upon exposure during travel in particular when departing from countries where oral whole cell/life-attenuated vaccines based on the Ty21a-strain are not available. Our data, however, does not argue against multiple subsequent vaccinations with the parental S. typhi Vi-capsular polysaccharide vaccines, especially as earlier studies also demonstrated a good tolerance of the parental vaccination [19]. Another option is to alternately vaccinate with the oral S. typhi Ty21a vaccine if available which may also provide immunoprotection against S. paratyphi [20,21] and offers a good alternative for subsequent vaccination after previous parental polysaccharide vaccine(s). According to the manufacturers’ instructions, re-vaccination with the oral/parenteral vaccines are recommended after 5/3 years, respectively [22–24]. A limitation of the study was the rather small sample size. To estimate the serological response following multiple re-vaccinations with S. typhi Vi-capsular polysaccharide vaccines in travellers further studies with larger samples sizes are desirable. Absolute antibody concentration are difficult to compare to other data published earlier [7,9], probably due to different inhouse tests and standard curves. We therefore calculated our data by comparison to an FDA reference sample to allow comparison to some data published earlier [5,6] and further studies to come. Yet, the internal validity of our study is not affected and findings are, therefore, appropriate to answer the respective research question of the present study. 5. Conclusion In conclusion, we were not able to demonstrate a relevant immunotolerance after multiple versus primary vaccination with S. typhi Vi-capsular polysaccharide vaccines.
L. Roggelin et al. / Vaccine 33 (2015) 4141–4145
Contributors LR, CDV, JFH and TR participated in patient recruitment and data collection. LR performed the statistical analyses and drafted the manuscript. JPC conceived of the study and participated in its design and coordination and helped to draft the manuscript. CDV, JFH, GDB significantly contributed to the protocol development and/or study implementation. All authors read and revised the manuscript and approved the final version. The analysis forms part of the doctoral thesis of LR. Conflict of interests statements CDV, JFH, GDB and JPC participated in industry-sponsored clinical trials that included typhoid fever vaccines. JPC has received consulting honoraries from industrial companies producing typhoid fever vaccines. LR and TR have no conflict of interest. Acknowledgements The authors would like to thank the entire staff at the Bernhard Nocht Center for Clinical Trials (www.bncct.de), in particular Mrs. Sabine Eberhardt and Mrs. Anja Wentzin, for their enduring and valuable support. References [1] Crump JA, Mintz ED. Global trends in typhoid and paratyphoid fever. Clin Infect Dis 2010;50:241–6. [2] Whitaker JA, Franco-Paredes C, del Rio C, Edupuganti S. Rethinking typhoid fever vaccines: implications for travelers and people living in highly endemic areas. J Travel Med 2009;16:46–52. [3] Klugman KP, Koornhof HJ, Robbins JB, Le Cam NN. Immunogenicity, efficacy and serological correlate of protection of Salmonella typhi Vi capsular polysaccharide vaccine three years after immunization. Vaccine 1996;14:435–8. [4] Acharya IL, Lowe CU, Thapa R, Gurubacharya VL, Shrestha MB, Cadoz M, et al. Prevention of typhoid fever in Nepal with the Vi capsular polysaccharide of Salmonella typhi. A preliminary report. N Engl J Med 1987;317:1101–4. [5] Lin FY, Ho VA, Khiem HB, Trach DD, Bay PV, Thanh TC, et al. The efficacy of a Salmonella typhi Vi conjugate vaccine in two-to-five-year-old children. N Engl J Med 2001;344:1263–9. [6] Szu SC, Hunt S, Xie G, Robbins JB, Schneerson R, Gupta RK, et al. A human IgG anti-Vi reference for Salmonella typhi with weight-based antibody units assigned. Vaccine 2013;31:1970–4.
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