Current rabies vaccines and prophylaxis schedules: preventing rabies before and after exposure

Travellers are probably the largest group in the general population to receive rabies pre-exposure prophylaxis. The dangerous consequences of the unavailability of rabies immune globulin in many countries could be ameliorated if pre-exposure rabies vaccination were practised more widely, especially in children, living in dog rabies enzootic countries. The WHO has recommended several different regimens for post-exposure prophylaxis, while individual countries decide on protocols for local use. Intramuscular regimens are expensive and waste vaccine. Although failure to receive vaccine is usually the due to the cost, the economical potential of intradermal vaccination has still not been realised 19 years after its introduction. The currently recommended 2-site intradermal post-exposure regimen is not economical for use in rural areas where 80% of Indian rabies deaths occur. Most countries using it demand higher potency vaccine, indicating that they do not have complete confidence in the method. This intradermal regimen has only been used where immunoglobulin is likely to be available for severely bitten patients. Increased intradermal doses are sometimes used for selected patients. Provision of economical rabies prophylaxis can be improved. Decisions to change recommendations should take account of the immunological, financial, practical and logistical aspects of dog bite treatment in remote areas.     

Early antibody responses to rabies post-exposure vaccine regimens

The aim of post-exposure rabies vaccine treatment is to induce immunity, measured as neutralizing antibody, as fast as possible. This is especially important in the tropical rabies-endemic areas where simultaneous passive prophylaxis with hyperimmune serum is not practicable in the majority of cases. We compared the rate of production of antibody during the first two weeks, by six vaccine regimens in 118 subjects using two tissue culture vaccines, human diploid cell strain vaccine (HDCSV) and purified Vero cell rabies vaccine (PVRV). No antibody was detected on day 5. On day 7, the highest seroconversion rate was seen in subjects given HDCSV intramuscularly at two sites on days 0 and 3 (7 of 15), but this was not significantly different from the group with the lowest rate: the conventional single-site intramuscular regimen. All subjects had antibody by day 14, at which time the highest geometric mean titer was in the group vaccinated with 0.25 ml doses of diploid cell vaccine given subcutaneously at eight sites. This regimen, together with the standard single-site diploid cell vaccine and an eight-site intradermal regimen of the same product gave significantly higher titers than the two-site intramuscular regimens of either product. No single immunization schedule emerges as best, so the speed of antibody response, economy, and the skill needed for intradermal injection should be considered when deciding on the optimum regimen for use in a particular geographic area.     

Failure of pre- and postexposure rabies vaccinations in a child infected with HIV.

We report the case of a 6-y-old HIV-infected girl with severe immune deficiency who failed to respond to intramuscular pre-exposure rabies vaccination using human diploid cell rabies vaccine on days 0, 7 and 28. She also failed to respond to an intradermal postexposure rabies regimen using purified verocell rabies vaccine at 4 sites on days 0, 3 and 7 and at 2 sites on days 30 and 90 (double the usual regimen). Sequentially monitored rabies neutralizing antibody titers were below the WHO minimum acceptable level (> 0.15 IU/ml) in all specimens. Rabies prevention in HIV-infected persons with severe immune suppression requires further study.     

Immunogenicity and effectiveness of post-exposure rabies prophylaxis with a new chromatographically purified Vero-cell rabies vaccine (CPRV): a two-stage randomised clinical trial in the Philippines

Recent improvements in chromatographic purification procedures have made it possible to develop a new chromatographically purified rabies vaccine (CPRV) by further purifying the current rabies vaccine prepared from Vero-cell culture (PVRV) (Verorab; Pasteur Merieux Connaught). The immunogenicity and effectiveness of post-exposure rabies prophylaxis with this new vaccine were evaluated in a two-stage clinical trial conducted in the Philippines. In both study stages. post-exposure treatment consisted of five injections of vaccine [(D)ays 0, 3, 7, 14, 28], together with a dose of rabies immunoglobulin (RIG) of equine or human origin on D0. In stage 1, 231 subjects with low-risk rabies exposure (WHO category I or II), and who had a negative ERIG skin test, were treated with either CPRV (n = 114) or PVRV (n = 117). By D14, all subjects in each group had achieved rabies antibody titres over ten times that recommended by the WHO as indicating seroconversion (> or = 0.5 IU/ml). The kinetics of the immune response to vaccination were very similar in the two groups, and at D28, the immunogenicity of CPRV was equivalent to that of PVRV (one-sided equivalence test). Following these positive results, 132 subjects with severe rabies exposure were included in the second stage of this trial. All were scheduled to receive four vaccine doses with CPRV. After D14, only those 57 patients with confirmed rabies exposure (animal with positive FA test) and seven patients for whom rabies exposure could not be excluded (animal lost or not tested) completed the treatment and were followed for one year to assess survival. After 1 year, 62 patients treated for confirmed or possible severe rabies exposure had been examined and were still alive. Two patients contacted by letter and telephone confirmed good health 7 and 16 months after exposure. No severe local or systemic reactions were reported in either stage of the study, and no treatment-related serious adverse event occurred. This two-stage clinical trial attests to the safety and satisfactory immunogenicity of CPRV in post-exposure rabies treatment, and confirms the effectiveness of a new rabies vaccine in patients with severe confirmed exposure.     

Simulated post-exposure rabies vaccination with purified chick embryo cell vaccine using a modified Thai Red Cross regimen.

OBJECTIVES: Currently, two intradermal regimens for the administration of cell culture rabies vaccines are approved by the WHO for rabies post-exposure prophylaxis: the two site Thai Red Cross regimen (TRC) and the eight site regimen. For the TRC regimen the volume of vaccine recommended per dose is 0.1 ml of purified Vero cell rabies vaccine (PVRV) and 0.2 ml of purified chick embryo cell vaccine (PCEC). The objective of the present study was to evaluate comparatively the immune response to PCEC and PVRV vaccines administered by the TRC regimen using a uniform dose of 0.1 ml of vaccine. METHODS: Forty-two subjects received TRC regimen (2-2-2-0-1-1) with 0.1 ml of PCEC vaccine and 38 subjects received the same regimen with PVRV. The rabies neutralizing antibody response in these subjects on days 10, 28, 90 and 180 was determined by the standard mouse neutralization test (MNT). RESULTS: There was adequate antibody response with both the vaccines and 100% seroconversion was observed by day 10. Furthermore, the antibody titers obtained with PCEC did not differ significantly from those obtained with PVRV on all days tested (p > 0.05). CONCLUSIONS: It can be concluded from the results that an adequate antibody response can be obtained with PCEC vaccine when administered by the TRC regimen even after reducing the quantity of vaccine from 0.2 ml to 0.1 ml per intradermal dose. The feasibility of using this regimen in true post-exposure cases needs to be further evaluated.     

Preventing rabies with the Verorab vaccine: 1985-2005 Twenty years of clinical experience

Purified rabies vaccine cultured on Vero cells (Verorab, sanofi pasteur) is WHO-approved for pre- and post-exposure prophylaxis by intradermal and intramuscular routes. During 20 years of use, over 40 million doses of Verorab have been administered in more than 100 countries. No serious adverse event due to Verorab has been reported in clinical trials involving 3937 persons, and Verorab is better tolerated than human diploid cell vaccine (HDCV). Pre-exposure prophylaxis is confirmed immunogenic in 1437 subjects by all routes, with prompt responses following boosting; Verorab boosts effectively subjects pre-immunized with HDCV. Unlike HDCV, Verorab is not associated with post-boosting serum sickness. In the absence of data in immunodeficient/HIV-positive individuals, pre-exposure immunization is urged as early as possible. Essen, Zagreb, Thai Red Cross Intradermal (TRC-ID) and other post-exposure intramuscular and intradermal regimens are documented. Two thousand one hundred and eighty-three subjects received post-exposure prophylaxis, including 874 high risk, severe or confirmed rabid attacks. Co-administration of rabies immune globulin (RIG) does not affect neutralizing antibody levels when Essen or TRC-ID regimens are employed; levels are lower with the Zagreb regimen. Verorab has been administered safely and effectively post-exposure to 251 pregnant women, without any increase in congenital malformations or spontaneous abortions. From a pediatric perspective, safety and efficacy have been demonstrated in 759 children (0-15 years). Intradermal post-exposure Verorab is an effective and inexpensive option for developing countries. Inadvertent subcutaneous administration does not reduce immunogenicity. WHO already strongly recommends the replacement of nerve tissue vaccines with modern vaccines. Extensive clinical experience supports the use of Verorab for intramuscular and intradermal pre- and post-exposure prophylaxis, including in special situations.     

Anti-rabies antibody titers among subjects who received rabies post-exposure prophylaxis with foreign-made rabies vaccines at the beginning and followed with Japanese rabies vaccine

Recently travelers who were bitten by possibly rabid animals in rabies endemic regions and returned to Japan have increased in number. About half of them received rabies post-exposure prophylaxis (RPEP) with one or more doses of foreign-made rabies vaccines (FRV) in the local medical institutions. FRV, however, are not available in Japan so we have to continue the RPEP with Japanese rabies vaccine (JRV). It has not been demonstrated that an anti-rabies antibody induced with JRV following Vero cell rabies vaccine (PVRV) or chick embryo cell rabies vaccine (PCEC) could be high enough to prevent clinical rabies. We examined anti-rabies antibody (ARA) titers among the subjects visited our vaccine clinic to receive RPEP and obtained results as follows: the ARA titers after a total of 5 doses of PCEC or PVRV and JRV were high enough to prevent clinical rabies as after 5 doses of JRV. However, ARA titers obtained after receiving one dose of PVRV and 2 doses of JRV seemed lower than those produced after one dose of PCEC and 2 doses of JRV or 3 doses of JRV. To accelerate antibody production, consequently, the simultaneous intradermal and subcutaneous injection method of rabies vaccine may be applied to those who were bitten in their hands or head by possibly rabid animals and received only one dose of PVRV in rabies endemic regions.     

Epidemiology and prevention of animal bite and human rabies in a rural community-One health experiment

ObjectiveTo estimate the incidence of human rabies and animal bite/exposure; to describe the post exposure prophylaxis received by animal bite/exposure cases; to assess the safety and immunogenicity of rabies vaccine (purified chick embryo cell vaccine) administered as pre-exposure vaccination for school children and risk groups by intradermal route in the rural community and to demonstrate a decrease in the incidence of human rabies and animal bite/exposures through implementation of one health experiment.MethodsThis prospective interventional study was conducted over a period of 2 years (December 2009-November 2011) in a rural area near Bangalore, Karnataka, South India and consisted of six villages (project villages), three villages were identified as study villages with active interventions (Implementation of rabies awareness activities, post exposure prophylaxis, pre-exposure intradermal rabies vaccine) and three villages as control villages without any active interventions.ResultsA majority of the animal bite cases were category III exposures and all of them had received rabies immunoglobulin and anti-rabies vaccine as per WHO recommendation. A majority received 3 to 5 doses of vaccine. Three hundred and sixty eight subjects had received pre-exposure intradermal rabies vaccination thrice on days 0, 7 and 28 d.ConclusionsNo human rabies case was reported during the study period and there was 30% decrease in animal bite/exposure cases in study villages after the one health experiment project was implemented. Pre-exposure vaccination was safe and immunogenic.     

Intradermal immunization with reduced doses of human diploid cell strain rabies vaccine: evaluation of antibody response by ELISA and mixed hemadsorption test

The antibody response to the rabies human diploid cell strain vaccine was compared after pre-exposure immunization with 0.1 ml intradermal (i.d.) and 1.0 ml subcutaneous (s.c.) vaccination. After primary immunization, 2 doses of vaccine 1 month apart, all vaccinees in the two groups had antibody titers detectable by ELISA. However, the mean antibody titer after the 0.1 ml i.d. doses (5.9 EU/ml) was half of what was obtained after the 1.0 ml s.c. doses (12.2 EU/ml). Likewise, though all vaccinees responded on the 1-year booster dose the mean antibody level after i.d. vaccination (8 EU/ml) was 2.5 times lower than after 1.0 ml s.c. dose (21.5 EU/ml). At 1 year 70% of the vaccinees had detectable antibody levels irrespective of vaccination route. A few individuals responded to one of their i.d. doses with only minor titer rises which is supposed to be due to inadvertent s.c. injection of the i.d. dose.     

Intradermal pre-exposure rabies immunisation in New Zealand

BACKGROUND: Rabies is a fatal infection and immunisation is important to consider in those travellers going to rabies endemic areas. In those at high risk, a course of three immunisations may be given by the intramuscular (IM) or intradermal (ID) route, both of which are approved by the World Health Organization (WHO) and the Centers for Disease Control (CDC). Little is known in the New Zealand context regarding the effectiveness of pre-exposure ID rabies immunisation. METHODS: The data was collected prospectively on all travellers requiring the immunisation from July 2001 to September 2003 in Auckland. The standard WHO rabies immunisation protocol was used with three ID injections of 0.1 ml, given on days 0, 7, and 21 or 28 with a booster after 12 months. The vaccine used was the Pasteur Merieux human diploid cell vaccine (HDCV) or the Rabipur Purified chick embryo cell (PCEC) vaccine. Both vaccines are approved by the WHO and the CDC, and are interchangeable. Serology was performed approximately 2 weeks after completion of the primary immunisation course or after a booster, wherever possible. Antibody levels were measured using EIA, and levels of >0.5 IU/ml were considered protective. RESULTS: Of the 263 travellers assessed in this study, 125 were males and 138 were females. The mean age of the cohort was 34.8 years (SD=11.7). There were not found to be any statistically significant correlations between age and antibody levels neither was there any significant association between gender and antibody levels. In addition to the sample group, a further 12 travellers had rabies serology performed but were excluded from the study because they had IM vaccines as part of their primary course. Whilst rabies serology ranged from 0.2 to 27.9 IU/ml in the study cohort, the mean antibody level for the group was 4.7 IU/ml (SD=4.1 IU/ml). The mean antibody level for males was 4.3 IU/ml (SD=3.3), and for females, 5.2 IU/ml (SD=4.6). Of the 263 travellers, all had some level of detectable antibodies. The overall seroconversion rate was 95.1%. CONCLUSIONS: ID rabies immunisation appears effective, when given according to the standard WHO protocol, in New Zealand. ID rabies immunisation is also more affordable for travellers, especially those on a restrictive budget. ID rabies immunisation can continue to be recommended, particularly where follow-up serology can be done before travel and where there are staff who are experienced in ID immunisation.     

Practical management of rabies and the 1982 outbreak in Zorzor District, Liberia

A rabies outbreak in Zorzor District, Liberia, in 1982 resulted in 31 known bitten and 12 known exposed patients. Human diploid cell strain (HDCS) vaccine was used to vaccinate 40 patients. Of these, 34 were vaccinated at Curran Lutheran Hospital, Zorzor, Liberia, mostly by the intradermal (i.d.) route. Five of 28 bitten patients who started their vaccinations did not complete the 4-dose course, including a 16-year-old boy who did not return after the first injection and later died of rabies. There were also 2 deaths in 3 known bitten but unvaccinated patients. None of the 23 bitten who received 4 doses of HDCS vaccine contracted rabies. The i.d. route was also used for pre-exposure prophylaxis. This method of vaccination is less expensive than the intramuscular route and in our clinical setting we would not have been able to vaccinate all the patients without using it. A practical approach to rabies vaccination in a developing country and the technique of intradermal vaccination are discussed.     

A new Vero cell rabies vaccine: results of a comparative trial with human diploid cell rabies vaccine in children.

We evaluated the immunogenicity and safety of a chromatographically purified rabies vaccine (CPRV) compared with human diploid cell rabies vaccine (HDCV) after pre-exposure immunizations (both primary and booster). Intramuscular doses of either 0.5 mL of CPRV or 1.0 mL of HDCV were given to 400 schoolchildren on days 0, 7, 28, and 365 (booster). Adequate titers of antibody (> or = 0.15 IU/mL, as defined by the Centers for Disease Control and Prevention) were observed in serum samples from all children 14 days after primary immunization with CPRV and HDCV; the antibodies persisted in all but one child up until 1 year. Fourteen days after the primary immunization series (day 42) and 7 days after booster immunization (day 372), all children had antibody titers of > or = 0.5 IU/mL. Local and systemic reactions after primary and booster immunizations occurred significantly less frequently in the CPRV group. A severe allergic reaction (angioedema) was reported in only one child after booster immunization with HDCV. CPRV has adequate immunogenicity for primary and booster pre-exposure immunizations in children and has a better safety profile than does HDCV.     

Immunization with a human diploid cell strain of rabies virus vaccine: two-year results

Antibody responses following primary vaccination with 1.0 ml of intramuscularly (im) or 0.1 ml of intradermally (id) administered human diploid cell rabies virus vaccine were observered for two years. Three primary doses of vaccine were given to 77 volunteers on days 0, 28, and 56. An antibody response was detected in all vacinees after a single dose; at one month, the response in the group that received vaccine id was identical to that in the group that was given vaccine im, although only 1/10th of the dose of vaccine was used. After the second and third doses, the antibody responses were higher with the primary im regimen; this difference was significant at two, three, and 12 months when the geometric mean titers of antibody were twofold higher for im than for id vaccination. The antibody responses to a booster dose of vaccine administered to randomly grouped volunteers by the subcutaneous or id route at six, 12, or 24 months were similar irrespective of the method of primary immunization but were greater with increasing intervals between primary and booster doses.     

Economical multi-site intradermal regimen with purified chick embryo cell vaccine (Rabipur) prevents rabies in people bitten by confirmed rabid animals.

OBJECTIVE: To determine the efficacy of a cost-effective multi-site intradermal regimen with purified chick embryo cell vaccine (PCECV, Rabipur) in preventing rabies in people bitten by confirmed rabid dogs. METHODS: Thirty-two people of different age groups who were severely bitten by confirmed rabid dogs were immunized with PCECV using the WHO recommended multi-site intradermal regimen of 0.1 mL of vaccine at eight sites on day 0, at four sites on day 7, and at one site each on days 28 and 90. In addition, passive immunization with human or equine rabies immunoglobulin was administered to 22 of these people before administering vaccine. They were followed for up to 3 years with periodic estimation of neutralizing antibody levels in their serum by mouse neutralization test (MNT). RESULTS: There was an excellent immune response with more than protective titers (>0.5 IU/mL) on all days tested up to the end of the 3-year observation period. More significantly, protective titers were seen in all subjects by day 7. Only minimal side effects were observed. All the patients were doing well at the end of the 3-year observation period, which is generally considered to be the maximum incubation period for rabies in humans. CONCLUSIONS: It can be concluded that this multi-site regimen with or without passive immunization has prevented the development of rabies encephalitis in these people bitten by confirmed rabid dogs. This should encourage more such studies, so that this cost-effective economical regimen with safe and potent cell culture vaccines can replace highly reactogenic neural tissue-derived Semple vaccine in developing countries such as India.     

人用狂犬病疫苗肌肉注射免疫程序研究进展

狂犬病尚无有效治疗方法,其预防措施主要为暴露前或暴露后接种人用狂犬病疫苗。随着狂犬病疫苗生产工艺的发展,疫苗质量不断提高,其免疫程序也在不断改进。目前,国内普遍采用肌肉注射方法进行狂犬病疫苗接种,暴露前免疫程序为在第0、7、21或28天(0、7、21或28 d)各注射1剂疫苗;暴露后免疫程序为5针法和2-1-1法,再暴露免疫程序则根据第1次暴露后免疫后间隔时间的不同,接种不同剂次的疫苗。2018年《狂犬病疫苗:WHO立场文件》根据狂犬病研究的最新进展,对狂犬病暴露预防免疫程序进行了简化。本文将在新立场文件的基础上,对国内外狂犬病暴露预防处置程序研究进展进行总结,并就我国狂犬病疫苗免疫程序与新立场文件倡导的免疫程序间存在的差异及改进方案加以讨论。     

Antibody response after a four-site intradermal booster vaccination with cell-culture rabies vaccine.

The current World Health Organization recommendation for booster vaccination of previously immunized individuals with potential exposure to rabies is two doses of vaccine intramuscularly or intradermally on days 0 and 3. We report responses to two types of postexposure treatment of healthy individuals who had received preexposure rabies vaccination 1 year previously. Group A individuals received four intradermal doses (one-fifth of the diluent volume of vaccine per dose) on day 0, and group B individuals received two intramuscular doses on days 0 and 3. Immunogenicity of the two booster regimens was assessed by titrating the amount of neutralizing antibody (Nab). We found that the booster doses of vaccine produced remarkable responses in all subjects. Nab titers of > or = 0.5 IU/mL (acceptable antibody level for protection against rabies) were detected in all subjects on day 14, and they were shown to be consistently high 1 year after the booster vaccination. We also found that the Nab titers for group A were significantly higher (two- to eightfold) than those for group B on days 5, 14, 150, and 360 after the initial booster vaccination (P < .05). Our study shows that the four-site intradermal booster regimen with use of one-fifth of the diluent volume of cell-culture rabies vaccine on day 0 is associated with a significantly higher antibody response than is the conventional booster regimen for subsequent postexposure rabies treatment of individuals who have received preexposure rabies vaccination with cell-culture rabies vaccine 1 year previously.     

A case received pre-exposure immunization against rabies by intradermal injection of rabies vaccine because of allergic reaction to the component of the vaccine]

A female, 25 years of age, came to our clinic to receive pre-exposure immunization against rabies. In another hospital she was tested to find out whether she was allergic to the components of rabies vaccine (PCEC) manufactured by the Chemo-Sero-Theraptic Research Institute (Kaketsuken) by cutaneous reaction using a 2,000-fold diluted PCEC. She showed a positive reaction. In our clinic she was again examined by skin test using 0.1 ml of 10-fold diluted PCEC. She showed wheal and flare reaction. Further we tested using 0.05 ml and 0.1 ml of non-diluted PCEC. Her skin reaction did not increase by several mm in diameter. So we decided to immunized her against rabies with intradermal injections of PCEC instead of subcutaneous injections that is indicated by the manufacturer. The second intradermal injections were done to right and left forearms a week later. Then the third shot was given 4 weeks after the second. At 2 weeks after the third injection her blood sample was taken to measure anti-rabies antibody titer by ELISA method with Platelia rabies kit (Diagnostic Pasteur, France). She had 6.7 U/ml of anti-rabies ELISA antibody that was much higher than the protective level (0.5 IU/ml) officially recognized by WHO. Therefore, it is concluded that she had produced sufficiently high level of anti-rabies antibody with intradermal injection of PCEC. It is reasonably recommended to investigate further if the intradermal injection of PCEC will be an effective method as a pre-exposure immunization against rabies.     

Immune response after rabies vaccine in a kidney transplant recipient

A 48-year-old male kidney-transplant recipient was bitten by a rabid dog. His immunosuppressive treatment consisted of cyclosporine 60 mg b.i.d., mycophenolate mofetil (MMF) 250 mg t.i.d., and prednisone 5 mg. After wound care, he received 5 doses of purified vero cell rabies vaccine on days 0, 3, 7, 14, and 28, and human rabies immunoglobulin, according to international guidelines. Adequate levels of rabies virus neutralizing antibodies were observed after the administration of the third vaccine dose. However, a decrease of antibody titer was detected by day 28. Immunosuppressive medication was minimized, withdrawing MMF and reducing the dose of cyclosporine. Booster doses of the same vaccine were administered on days 38, 41, 45, 52, and 66. Adequate neutralizing antibody response was recovered during the ensuing 12 months, under reduced immunosuppression. Nineteen months after the incident, the patient remains with good graft function and is asymptomatic for rabies. It remains to be determined whether the attained immune response was either the result of the booster vaccinations or the reduction of immunosuppression alone. Nevertheless, such an outcome would have been possible only with the combined management strategy implemented.     

The early kinetics of the neutralizing antibody response after booster immunizations with human diploid cell rabies vaccine

Persons immunized in developing countries were recently shown to have low titers after pre-exposure immunization with human diploid cell rabies vaccine (HDCV). An investigation into the response to HDCV boosters was conducted to determine if immunologic sensitization had occurred and if there was a response difference in persons immunized in and outside of the United States. Intramuscular (im) booster doses of vaccine were administered to 113 persons previously immunized outside the United States and 47 persons immunized in the United States. The post-exposure booster regimen of a single 1.0-ml im booster, as recommended by the World Health Organization for all but the most severe bites, produced a one-dilution (5-fold) rise in antibody titer in 14 (11%) of 123 persons tested 5 days after booster and in 56 (89%) of 63 persons studied 7 days after booster. Persons immunized in the United States and those immunized outside the United States had similar responses. Persons with low pre-booster titers were more likely to exhibit a 5-fold rise in antibody titer 5 days after booster (P = 0.03) than persons with higher pre-booster titers. The post-exposure booster regimen of 2 1.0-ml im doses (one each on days 0 and 3), recommended in the United States, produced a more rapid response than the single booster regimen in only some persons; a 5-fold response occurred in 6 (50%) of 12 persons 5 days after booster.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pre-exposure rabies immunization with human diploid cell vaccine: decreased antibody responses in persons immunized in developing countries

In November 1982, a U.S. Peace Corps volunteer in Kenya completed pre-exposure rabies prophylaxis with a standard 3 dose intradermal (ID) series of human diploid cell rabies vaccine (HDCV). In May 1983, she was bitten by a dog and died of rabies 3 months later. An initial investigation revealed that the patient, as well as 9 of 11 others immunized at the same time, had no rabies antibody titers (less than 1:5). We therefore instituted investigations into the immunogenicity of pre-exposure HDCV both in the United States and in developing countries. A serosurvey revealed unexpectedly low rabies titers in both Peace Corps volunteers and others immunized in developing countries. Antibody titers measured 2-3 weeks after ID immunization were compared in 9 groups totaling 271 persons in the United States and Kenya. There was no statistically significant difference in antibody titers in the 6 U.S. groups immunized from 1980-1984 (P greater than 0.15); however, groups immunized in the United States had significantly higher titers than a group of Kenyan nationals (P less than or equal to 0.0001), and the Kenyans had significantly higher titers than 2 Peace Corps groups immunized in Kenya (P less than or equal to 0.0001). No single hypothesis proposed (laboratory error, vaccine potency, vaccination technique, or specific immune suppression) accounted for the observed differences. Although we cannot fully explain the poor response to HDCV, it is probably due to multiple factors. We conclude that persons immunized with ID pre-exposure HDCV in developing countries should have rabies antibody titers determined to ensure their seroconversion; for persons immunized in the United States, such titers need not be routinely determined.