by Jean Lang, a Emmanuel Feroldi, a and Nguyen Cong Vien b a Sanofi Pasteur, Marcy L etoile, France

Transcription

1 Pre-exposure Purified Vero Cell Rabies Vaccine and Concomitant Routine Childhood Vaccinations: 5-year Post-vaccination Follow-up Study of an Infant Cohort in Vietnam by Jean Lang, a Emmanuel Feroldi, a and Nguyen Cong Vien b a Sanofi Pasteur, Marcy L etoile, France b Center of Pediatrics, Development and Health, Children s Hospital No. 2, Ho Chi Minh City, Vietnam Summary Children have a high risk of exposure to rabies in countries where the disease is endemic. This prospective, 5-year study followed two groups of children who had received diphtheria, tetanus, whole-cell pertussis and inactivated poliomyelitis vaccine (DTP-IPV) at 2, 3, 4 months and 1 year (Group B) or concomitant with three doses of purified Vero cell rabies vaccine (PVRV), given at 2, 4 months and 1 year (Group A). Antibody determinations were made annually for 5 years. Data were available from a total of 72 subjects; 30 in Group A and 32 in Group B. In Group A, the percentage of patients immunized against rabies (anti-rabies 0.5 IU/ml) decreased from 0% after the third vaccination to 63%, 5 years later. After 5 years, 93.8% in Group A and 96.7% in Group B had seroprotective diphtheria antibody titers 0.01 IU/ml, and all subjects had anti-polio (type 1, 2 and 3) seroprotective titers 5 1:dil. We conclude that co-administration of PVRV with DTP-IPV elicited protective antibody concentrations to all antigens that persist for at least 5 years, with continued protection against rabies in over 60% of subjects. These results are consistent with integration of pre-exposure rabies vaccination into the Expanded Program on Immunization (EPI) in countries where rabies is endemic. Key words: concomitant DTP-IPV, Expanded Program of Immunization, intramuscular, purified Vero cell rabies vaccine, rabies pre-exposure immunization, routine childhood vaccination. Introduction Worldwide, rabies causes at least deaths a year, with more than half occurring in Asia [1]. In countries such as Vietnam and Thailand, where rabies is enzootic, almost half of rabies patients are children younger than 15 years of age [2,3]. Children are at a particular risk of rabies exposure from animal bites owing to their unwariness of animals Acknowledgement This study was funded by Sanofi Pasteur, France. The authors wish to acknowledge Dr DQ Hoa and Dr CP Thien for their participation in this study, Dr V Delore for her close follow up of the investigation and C Weinberger for assistance in preparing this article. Correspondence: Jean Lang, Sanofi Pasteur 1541, Avenue Marcel Merieux 69280, Marcy l Etoile, France. <jean.lang@sanofipasteur.com>. and limited ability to fend off animal attacks. In addition, children s stature puts them at an increased risk of severe bite injuries to the face, head and neck, regions that are especially susceptible to infection by the rabies virus and have the shortest viral incubation periods [4 6]. Rabies almost invariably leads to a fatal encephalomyelitis once signs of disease occur. Individuals who have come into contact with a rabid animal require rapid post-exposure treatment with rabies vaccine or a combination of vaccine and rabies immunoglobulin (RIG) to prevent the virus from reaching the central nervous system. In Vietnam alone, post-exposure treatments were reported in 2004 [2,7] Use of the highly reactogenic suckling mouse brain vaccine (SMB, Fuenzalida) was discontinued in Vietnam in The type of post-exposure treatment required depends on an individual s immunization status for rabies. Patients who have been given pre-exposure rabies vaccination, can be treated with a simplified post-exposure regimen consisting of two booster ß The Author [2007]. Published by Oxford University Press. All rights reserved. For Permissions, please journals.permissions@oxfordjournals.org 26 doi:.93/tropej/fmm0 Advance Access Published on 29 November 2007

2 doses, on the first day (D0) and the fourth day (D3) after rabies exposure; whereas, previously rabiesnaïve patients require a series of five doses as well as treatment with RIG, which is costly and often beset with supply problems in developing countries [1,8]. Intramuscular (IM) vaccination with purified Vero cell rabies vaccine (PVRV) is long recognized as a well-tolerated and effective pre-exposure prophylaxis for rabies [9,]. Integration of PVRV within the Expanded Programme of Immunization (EPI) for routine childhood immunizations in developing countries would offer a high degree of protection to toddlers and young children in rabies-enzootic regions. A randomized trial in 84 infants in Vietnam trial found that a two-dose PVRV primary series concomitant with routine administration of a combination vaccine containing diphtheria, tetanus, whole-cell pertussis and inactivated poliovirus vaccines (DTwP-IPV) was both immunogenic and well tolerated [11]. The infants had been randomly assigned to vaccination with either DTwP-IPV alone or DTwP-IPV and IM PVRV (DTwP- IPVþPVRV). All infants developed seroprotective antibody titers against all vaccine components, including rabies virus [11]. Of the infants vaccinated against rabies, 75% maintained seroprotective antirabies antibody titers (0.5 IU/ml) 1 year later. Following a third dose of PVRV given 1 year later, the seroconversion rate for rabies was 0%, and there was no evidence of the PVRV interfering with either seroconversion rates or geometric mean titer (GMT) for any of the other vaccines [12]. All vaccinations were reported to be well tolerated. This study evaluated the long-term immunogenicity of PVRV vaccine when given as part of the routine childhood vaccination schedule followed in Vietnam. We monitored the seroprotection rates and persistence of neutralizing antibody titers for rabies, diphtheria and poliomyelitis annually over a period of 5 years following a third dose of PVRV and a fourth dose of DTwP-IPV given 1 year after completion of the primary series. We followed the same cohort of Vietnamese children who had enrolled in the earlier trial [11,12]. Materials and Methods Study design This was an open, single-centre, 5-year follow-up study of 84 Vietnamese children residing in Ho Chi Minh City, who had been randomized as infants to one of two primary vaccination series in 1995: either a single IM injection of DTwP-IPV at ages 2, 3 and 4 months into the anterolateral thigh plus concomitant IM injection of PVRV at ages 2 and 4 months into the contralateral thigh, or DTwP-IPV only at ages 2, 3 and 4 months. One year later, the children received injections of DTwP-IPV and PVRV or DTwP-IPV only, as per the randomization performed for the primary series. The PVRV (Verorab Õ ) and DTwP- IPV (Tetracoq Õ ) vaccines were produced and supplied by Pasteur Merieux, (now Sanofi Pasteur), Lyon, France. The study inclusion and exclusion criteria and the detailed characteristics of the vaccines used have been described elsewhere [11,12]. The study was conducted in accordance with the Good Clinical Practice of the World Health Organization (WHO) and the Declaration of Helsinki. No Independent Ethics Committee existed in Vietnam at the time of the study. The protocol of the initial study describing the primary vaccination series, booster and follow up was submitted to the Vietnamese Ministry of Public Health before the study commenced. Informed written consent was obtained from parents or guardians for the booster injections and the follow-up visits, before booster injections were initiated. Study population and follow up Children included in the follow-up study had to have completed the primary vaccination series within 15 months, received the appropriate 1-year injections, and attended at least one scheduled follow-up visit. Children who did not attend any scheduled follow-up visits following injection of the final dose, or for whom no information were available at the end of the study, were classified as lost to follow up. Five follow-up visits were scheduled at yearly intervals, with the first visit at 1 year and the final visit 5 years after the completion of vaccination. At each visit, a 6ml blood sample was collected for serological analysis. No vaccines were administered during the follow-up visits. Evaluation of immunogenicity The serological tests were performed by a clinical immunology laboratory of the vaccine manufacturer, located in Val de Reuil, France. Diphtheria antibodies were assayed by use of validated ELISA procedures, poliomyelitis-neutralizing antibodies by use of seroneutralization techniques with HEPII cells and rabies-neutralizing antibodies by use of a rapid fluorescent focus inhibition test (RFFIT) on BHK21 cells. International reference sera were used to express antibody titers in IU/ml (diphtheria and rabies) or as an inverse of dilution (poliomyelitis). Details of the assay procedures have been previously reported [11,12]. Seroprotective antibody titers were defined as follows: anti-diphtheria antibodies 0.01 IU/ml, seroneutralizing poliomyelitis antibody titer 5 (1/dil), anti-rabies antibodies 0.5 IU/ml. Safety evaluation All children were monitored for serious adverse events (SAEs) during the annual follow-up visits, and discontinuation because of SAE was recorded. Journal of Tropical Pediatrics Vol. 55, No. 1 27

3 TABLE 1 Subject characteristics at the beginning of the 5-year follow-up period and numbers of assessable children during scheduled annual visits DTP-IPV only Statistical analysis The statistical data analysis was descriptive. Percentage rates of seroprotection GMT and twosided 95% confidence intervals (CI) for them were calculated for each valence at each follow-up visit. Antibody titers observed 2 weeks following the completion of vaccination [11,12] were used as baseline values. Results DTP-IPVþPVRV Age (years, SD) 2.42 (0.09) 2.43 (0.06) Sex (% male) Children (n) per visit a Booster vaccination b Year Year Year Year Year Lost to follow-up 4 6 a Number of children assessable during each follow-up visit. b PVRV, Primary vaccination at 2 and 4 months of age; third dose (booster) 1 year later; DTwP-IPV, Primary vaccination at 2, 3 and 4 months of age; fourth dose (booster) 1 year later. Subject disposition Of the 76 infants who received 1-year booster injections in 1996, a total of 72 infants (51.4% boys, 48.6% girls) participated in this 5-year followup study. Thirty-six children in each group attended at least one scheduled follow-up visit. A total of 62 children completed all the scheduled study visits during the 5-year follow-up period. Ten children (four in the DTwP-IPV only group, six in the DTwP- IPVþPVRV group) did not attend the final followup visit. Subject characteristics at the start of the follow-up period and number of children assessed during each scheduled visit are detailed in Table 1. Immunogenicity The changes in GMT and seroprotection rates over time are represented graphically in Figs 1 3 and in Table 2. Antibody titers and seroprotection rates obtained 14 days after the third dose of PVRV and the fourth dose of DTwP-IPV given previously to the same group of children [12] are included as the baseline values for the 5-year follow up. Anti-rabies. At 5 years post-vaccination, the GMT [95% CI] for anti-rabies antibody was IU/ml [0.472; 1.20] in the DTwP-IPVþPVRV group. As observed for the other antigens, the GMTs [95% CI] for anti-rabies antibody fell rapidly over the first year and decreased gradually thereafter. The fold decrease in GMT was 7.7 over the first year of follow up, between 1.8 and 1.4 from years 2 to 4, but there was no further decrease in GMT between year 4 and the end of the study in year 5 (Fig. 1). The percentage of children with seroprotective antibody titers against rabies (0.5 IU/ml) decreased from 0% for 14 days after the 1-year booster injection was given, to 89.7% (26/29) over the next 2 years. Five years following the booster vaccination, the majority of children (63.3%, 19/30) remained seroprotected to rabies (Table 2). Anti-diphtheria, tetanus, pertussis and polio. At the end of the 5-year follow-up period, the percentages of children with seroprotective anti-diphtheria titers (0.01 IU/ml) were similar in the DTwP- IPVþPVRV and the DTwP-IPV only groups, 96.7% vs. 93.8%, respectively. At 5 years, all 62 children remained seroprotected to all three poliomyelitis virus types. In both the DTwP-IPVþPVRV and the DTwP- IPV only groups, anti-diphtheria (Fig. 2) and antipolio GMT (Fig. 3) decreased, whereafter the annual decrease was minimal. At each scheduled follow-up visit, antibody titers against diphtheria and poliomyelitis remained above the seroprotective threshold values of 0.01 IU/ml and 5 (1/dil), respectively. Fiveyear post-vaccination GMTs [95% CI] for antidiphtheria antibody were IU/ml [0.061; 0.264] and 0.4 IU/ml [0.046; 0.236], respectively, for the DTwP-IPVþPVRV and DTwP-IPV only groups. The corresponding 5-year GMTs [95% CI] for antipoliomyelitis virus antibodies were 177 (1/dil) [125; 250] and 239 (1/dil) [167; 343], respectively, for type 1; 136 (1/dil) [94.4; 196] and 172 (1/dil) [119; 248], respectively, for type 2 and 129 (1/dil) [81; 206] and 182 (1/dil) [130; 255], respectively, for type 3. Safety No SAE were reported during the 5-year follow-up period. There were no withdrawals resulting from SAE. Discussion Previous studies in infants in Vietnam demonstrated high immunogenicity and safety without increase in reactogenicity during administration of the primary and 1-year booster vaccinations, supporting the integration of pre-exposure PVRV vaccination alongside routine childhood vaccinations (DTwP- IPV) following a 2-,3-,4-month schedule [ 12]. The results of this 5-year follow-up study confirm and extend these findings. The results show that the 28 Journal of Tropical Pediatrics Vol. 55, No. 1

4 Anti-rabies GMT (IU/mL) log Post booster 1 year 2 years 3 years 4 years 5 years FIG. 1. GMT and seroprotection rates (%) of antirabies antibodies in children receiving DTP- IPVþPVRV over 5 years of follow up beginning 2 weeks following administration of a third (booster) PVRV dose Seroprotection rate (%) A GMT (1/dil) Time since booster vaccination (years) B 000 GMT (1/dil) 00 0 type-1 Ab type-2 Ab type-3 Ab type-1 Ab type-2 Ab type-3 Ab GMT (IU/mL) DTP-IPV+PVRV DTP-IPV Time since booster vaccination (years) FIG. 3. GMT of anti-poliomyelitis antibodies (95% CIs) in children given DTP-IPV only or DTP- IPVþPVRV. Five-year follow up beginning 2 weeks following the fourth (booster) DTwP dose. (A) DTwP-IPV and (B) DTwP-IPV þ PVRV Time since booster vaccination (years) FIG. 2. GMT of anti-diphtheria antibodies (95% CIs) in children given DTP-IPV only or DTP- IPVþPVRV. Five-year follow up beginning 2 weeks following the fourth (booster) DTwP dose. concomitant administration of PVRV and DTwP- IPV has no obvious effect on the long-term seroprotection to diphtheria and poliomyelitis and seroprotective concentrations of anti-rabies antibodies persisted in the majority of children throughout the 5-years of follow up. All children evaluated in this follow-up study had seroprotective antibody titers against poliovirus types 1, 2 and 3; and more than 93% of these children had seroprotective titers of anti-diphtheria neutralizing antibodies, regardless of whether they had received DTwP-IPV alone or concomitantly with PVRV. In addition, the rabies seroprotection rate at 1 year after vaccination completion was 90%, and still exceeded 60% at 5 years. The marked decreases in the GMT of all antibodies (diphtheria, poliomyelitis and rabies) at 1 year were not unexpected, and were in line with the kinetics of neutralizing antibody response documented elsewhere [13,14]. Although this study was relatively small (n ¼ 72), its findings fit well with those of other, larger studies. The percentage of children in the combined vaccines group (DTwP-IPVþPVRV) who were protected against rabies at the end of follow up (63%) was comparable to that reported for adults in a large French study of over 300 individuals, who had received a two- (at 0 and 28 days) or three- (at 0, 7 and 28 days) dose IM pre-exposure PVRV regimen followed by a booster at 1 year. Five and years following the booster vaccination, 68 and 65% of adults, respectively, had titers of rabies-neutralizing antibodies considered to be protective [14]. Such long-lasting immunity generated by pre-exposure rabies vaccination has been reported in other studies of children and adults [13 15]. Collectively, the results of these studies give a strong indication that nearly all of the children evaluated in the present study who had protective antibody titers against rabies 5 years after their booster injection would likely remain protected for at least years, and most likely longer [13 15]. At the time the children in our study received the primary vaccination series, there were an estimated Journal of Tropical Pediatrics Vol. 55, No. 1 29

5 TABLE 2 Rabies Seroprotection rate in children receiving DTP-IPVþPVRV over 5 years of follow-up beginning 2- weeks following administration of the third PVRV dose Post-dose 3 1 year 2 years 3 years 4 years 5 years Anti-rabies titer 0.5 IU/ml 36/36 30/33 26/29 20/30 18/28 19/30 n/n, % rabies-related fatalities in Vietnam each year. Since then, there has been a dramatic rise in postexposure treatments from approximately to a year, which have undoubtedly contributed to a substantial fall in annual rabies-related deaths over the past decade to approximately 30 deaths in 2004 [7]. However, the cost of post-exposure treatments represents the single highest expenditure related to rabies [2]. A recent evaluation by the WHO of the rabies burden revealed that Asian countries accounted for 96.5% of the total global cost burden (US$580 million) associated with rabies [1]. Cost data are pertinent because most of the expenses of rabies treatment in developing countries are borne by patients, further underlining the need to increase pre-exposure vaccination in high-risk populations given the cost advantages associated with preexposure prophylaxis [16]. In patients requiring RIG, successful postexposure treatment depends on infiltrating as much as possible of the recommended dose of RIG into the depth of the wound and around the wound as is anatomically feasible [17]. For bite wounds that are located on the face, as they frequently are in small children, this can be notoriously difficult to accomplish. The fact that RIG is not needed for individuals who received a pre-exposure rabies vaccination simplifies the post-exposure procedure considerably and represents a major advantage of pre-exposure vaccination. Two routes of pre-exposure vaccination, IM or intradermal (ID), are available. In another study also concerning the integration of PVRV into a routine childhood schedule of immunizations, investigators compared DTwP-IPV-concomitant administration of PVRV given either as three reduced (0.1 ml) dose intradermal injections or a two-dose (0.5 ml) IM regimen in 240 Vietnamese infants. One month after the last injection of the primary vaccination series, neither of the PVRV vaccination regimens was reported to interfere with the efficacy of the DTwP- IPV vaccines, and all infants developed protective levels of anti-rabies antibody titers [18]. The use of a reduced-dose intradermal regimen (one-fifth of the IM PVRV dose) rather than an IM regimen suggests a straight-forward cost benefit. Indeed, a recent study into the cost of pre- vs. post-exposure treatment in Thai children concluded that the most cost-effective pre- and post-exposure schedules to be used in Thailand would be intradermal regimens [16]. However, Goswami and colleagues [19] have found that the true cost of rabies vaccination is not simply reflected by the price of the vaccine alone, as using one-fifth of the IM PVRV dose did not result in the predicted 50%, but only a 17%, cost reduction. Such savings must also be weighed against the expertise required to inject intradermal doses satisfactorily, which may be lacking in health centres not specialized in rabies vaccination. Within this context, the margin of safety linked to the administration of doses with smaller antigen content, vaccine wastage and infection risks associated with using the same vial for different patients or the conservation of opened vials must be considered. Finally, the actual cost differences between the two methods of administration will vary according to country-specific conditions. Further studies, especially long-term and costeffectiveness trials taking into account societal costs and expenses to the individual, are needed to clarify the role of low-dose intradermal vaccination regimens for routine rabies pre-exposure vaccination in terms of cost-saving options. In conclusion, the integration of a pre-exposure PVRV regimen of two IM doses at 2 and 4 months of age, followed by a booster at 1 year resulted in longterm persistence of seroprotective anti-rabies antibody concentrations in the majority of vaccinated children without interfering with the immune responses to concomitant DTwP-IPV immunizations. Including pre-exposure rabies vaccination in EPI countries such as Vietnam, with high rabies endemicity, is a realistic and practical option that can offer long-term protection against rabies to a majority of the population at the greatest risk of rabies infection, namely children. References 1. Knobel DL, Cleaveland S, Coleman PG, et al. Re-evaluating the burden of rabies in Africa and Asia. Bull World Health Organ 2005;83: Journal of Tropical Pediatrics Vol. 55, No. 1

6 2. Anonymous. WHO expert consultation on rabies. World Health Organ Tech Rep Ser 2005;931: Pancharoen C, Thisyakorn U, Lawtongkum W, et al. Rabies exposures in Thai children. Wilderness Environ Med 2001;12: Sriaroon C, Sriaroon P, Daviratanasilpa S, et al. Retrospective: animal attacks and rabies exposures in Thai children. Travel Med Infect Dis 2006;4: Tepsumethanon S, Tepsumethanon V, Wilde H. Risk of rabies after mammal bites in Thai children. J Med Assoc Thai 2002;85: Anonymous. Rabies vaccines. Wkly Epidemiol Rec 2002;77: Miranda ME. Rabies epidemiology, epidemiology, disease burden and disease burden and vaccine utilization in Asia vaccine utilization in Asia. Presented at the National Institute of Allergy and Infectious Diseases (NIAID) meeting Vaccines for Viral Infections in Developing Countries, 27, 28 July, 2006, Yokohama, Japan; Anonymous. Rabies vaccine update. Wkly Epidemiol Rec 2007;82: Dureux B, Canton P, Gerard A, et al. Rabies vaccine for human use, cultivated on Vero cells. Lancet 1986;2:98.. Jaiiaroensup W, Lang J, Thipkong P, et al. Safety and efficacy of purified Vero cell rabies vaccine given intramuscularly and intradermally (Results of a prospective randomized trial). Vaccine 1998;16: Lang J, Rongrre N, Plotkin S, et al. Randomised feasibility trial of pre-exposure rabies vaccination with DTP-IPV in infants. Lancet 1997;349: Lang J, Hoa DQ, Gioi NV, et al. Booster vaccination at 1 year with a rabies vaccine associated with DTP-IPV in infants living in a rabies endemic country. J Trop Pediatr 1999;45: Sabchareon A, Chantavanich P, Pasuralertsakul S, et al. Persistence of antibodies in children after intradermal or intramuscular administration of preexposure primary and booster immunizations with purified Vero cell rabies vaccine. Pediatr Infect Dis J 1998;17: Strady A, Lang J, Lienard M, et al. Antibody persistence following preexposure regimens of cell-culture rabies vaccines: -year follow-up and proposal for a new booster policy. J Infect Dis 1998;177: Suwansrinon K, Wilde H, Benjavongkulchai M, et al. Survival of neutralizing antibody in previously rabies vaccinated subjects: a prospective study showing long lasting immunity. Vaccine 2006;24: Chulasugandha P, Khawplod P, Havanond P, et al. Cost comparison of rabies pre-exposure vaccination with post-exposure treatment in Thai children. Vaccine 2006;24: Anonymous. World Health Organization: administration of rabies immunoglobulin. rabies/human/adminimmuno/en/printhtml (20 March 2007, date last accessed). 18. Lang J, Duong QH, Gioi NV, et al. Immunogenicity and safety of low-dose intradermal rabies vaccination given during an expanded programme on immunization session in Viet Nam: results of a comparative randomized trial. Trans R Soc Trop Med Hyg 1999;93: Goswami A, Plun-Favreau J, Nicoloyannis N, et al. The real cost of rabies post-exposure treatments. Vaccine 2005;23: Journal of Tropical Pediatrics Vol. 55, No. 1 31