Post-exposure intradermal antirabies vaccine: a cheaper alternative for developing countries

Intradermal (i.d.) human diploid-cell vaccine (HDCV) has been routinely used for post-exposure treatment of rabies at a rural mission hospital in central Thailand since 1979. Four 0.1 ml doses have been given over a fortnight, reconstituted vaccine being regularly stored for repeated use. No significant side effects have been encountered. Consistent antibody formation has been shown. In patients followed up for one year no case of rabies has been observed. Post-exposure intradermal HDCV is safer and more effective than nervous tissue vaccine and is of moderate cost. It should be more widely employed within the Third World.     

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.     

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.     

Intradermal influenza vaccine administered using a new microinjection system produces superior immunogenicity in elderly adults: a randomized controlled trial

BACKGROUND: Enhanced influenza vaccines are needed to provide improved protection for elderly individuals. The intradermal vaccination route was hypothesized to provide immunogenicity superior to that provided by the intramuscular vaccination route. METHODS: In a multicenter, randomized study, 1107 volunteers >60 years of age received intradermal trivalent inactivated influenza vaccine containing 15 or 21 microg of hemagglutinin per strain or intramuscular control vaccine. Intradermal vaccines used a novel microinjection system designed to ensure easy, convenient, consistent vaccination. The primary end points of the study were the strain-specific hemagglutination inhibition geometric mean titers (GMTs) noted 21 days after vaccination. Groups were compared using noninferiority and superiority analyses. RESULTS: For each strain, the GMTs noted in association with each intradermal vaccine were superior to those noted with the intramuscular control (adjusted P< .0001). Seroprotection rates, seroconversion rates, and mean titer increases were also superior for intradermally administered vaccine in all but one of the analyses undertaken. Systemic reactogenicity was comparable between routes. Local injection site reactions, particularly erythema but not pain, were more commonly associated with intradermal vaccination. CONCLUSIONS: For the first time, the intradermal vaccination route has been used to elicit immune responses significantly superior to those noted in association with the conventional intramuscular vaccination route. This was done using an easy-to-use, reliable microinjection system. This superior response is expected to enhance annual protection against influenza in this vulnerable population. TRIAL REGISTRATION: Clinicaltrials.gov registry number: NCT00296829.     

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.     

The present status of rabies vaccine development and clinical experience with rabies vaccine

Attempts to control human rabies have a long history: animal and human vaccines provide efficient weapons for prevention. In this presentation, we would like to consider the different rabies vaccines available for human use, and particularly the modern vaccines produced in cell culture. Rabies virus is considered as an unique virus, but in fact, 5 groups of rabies fixed strains are used throughout the world to produce human rabies vaccines: Pasteur, Beijing, Flury, Fuenzalida and SAD strains. The Pasteur-derived strains, designated PV or PM, are the most widely used for the production of traditional vaccines of the Semple or Suckling Mouse Brain (SMB) types, but also for the production of modern cell culture vaccines: Human Diploid and Purified Vero Cell vaccines (HDCV and PVRV). The different rabies vaccines should be classified according to the cell system used to cultivate the virus: animal systems are still employed to produce the old traditional vaccines-Semple and SMB-which continue to be produced in several countries; Primary cell systems, particularly Hamster Kidney and Chick embryo cells, are used; Cell lines are presently the most interesting approach for vaccine production. The use of the human diploid cell system permitted the development of the HDCV, the most widely distributed cell culture rabies vaccine, and today considered as the reference vaccine. The heteroploid VERO cell line was introduced in 1982 to the production of inactivated rabies vaccine; it retained all the advantages of the Human Diploid Cell system, while offering the possibility of the large scale industrial production of PVRV. For both HDCV and PVRV, production security is guaranteed by the existence of a master cell seed and working cell bank, with a complete history of the cell, a limited number of passages and permanent and total quality control of the cell substrate. The principal human rabies vaccines produced worldwide at present using cell culture are compared, in terms of their technical characteristics and their capacity economically to face worldwide vaccine needs. The greatest needs are today in tropical countries, where only a limited amount of modern cell culture vaccines are used.     

The Route of Administration of Rabies Vaccines: Comparing the Data

Cell culture rabies vaccines were initially licensed in the 1980s and are essential in the prevention of human rabies. The first post-exposure prophylaxis (PEP) vaccination regimen recommended by the World Health Organization (WHO) was administered intramuscularly over a lengthy three-month period. In efforts to reduce the cost of PEP without impinging on safety, additional research on two strategies was encouraged by the WHO including the development of less expensive production methods for CCVs and the administration of reduced volumes of CCVs via the intradermal (ID) route. Numerous clinical trials have provided sufficient data to support a reduction in the number of doses, a shorter timeline required for PEP, and the approval of the intradermal route of administration for PEP and pre-exposure prophylaxis (PreP). However, the plethora of data that have been published since the development of CCVs can be overwhelming for public health officials wishing to review and make a decision as to the most appropriate PEP and PreP regimen for their region. In this review, we examine three critical benchmarks that can serve as guidance for health officials when reviewing data to implement new PEP and PreP regimens for their region including: evidence of immunogenicity after vaccination; proof of efficacy against development of disease; and confirmation that the regimen being considered elicits a rapid anamnestic response after booster vaccination.     

Effect of inosiplex on the humoral and cell-mediated immune responses to intradermal human diploid cell rabies vaccine

Antigen-stimulated lymphocyte transformation was studied in recipients of intradermal human diploid cell rabies vaccine (HDCV). HDCV was administered intradermally at 8 different anatomical sites, 0.1 ml each, on day 0; followed by another 4-site injection on day 7. Rabies antigen-stimulated in vitro proliferative response was evident as early as 7 days after starting immunization. It reached a peak on day 14 and had declined by day 28. The cellular proliferative response preceded and roughly correlated with the antirabies antibody response. Simultaneous administration of inosiplex, an antiviral and immunopotentiating drug, during the first 10 days of intradermal HDCV immunization did not result in heightened antibody titres or cell-mediated immune response to the vaccine. The number of T cells and the lymphocyte proliferative response to phytohaemagglutinin in inosiplex-treated vaccinees were similarly not significantly different from untreated controls. Our results confirm other previous findings that a specific cell-mediated immune response can be consistently and rapidly induced by an intradermal regimen of HDCV immunization. The addition of inosiplex to this regimen did not enhance the humoral or cell-mediated immune responses to the vaccine. The apparent lack of immunostimulating effect of inosiplex in this setting may be the result of several factors such as the immunization schedule and the immunologic parameters examined.     

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.     

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.     

Pre-exposure prophylaxis in Peace Corps volunteers with intradermal human diploid cell rabies vaccine

The Peace Corps has had approximately 60 000 person/years of experience with rabies pre-exposure duck embryo vaccine (DEV) immunizations, which are required in 80% of volunteer assignments. Rabies exposure treatment rate is much higher in these areas than in the United States. One death from rabies has occurred despite pre-exposure injections. One death also occurred from serum hepatitis contracted in local emergency management of an anaphylactic reaction to duck embryo vaccine. A query to the Peace Corps field medical offices obtained reports of 21 serious reactions in approximately 8000 duck embryo immunizations. Two thirds of the reactions occurred with the first injection. Only a third of titres measured after four injections of DEV achieved a protective level of greater than or equal to 1:16. Because of these problems human diploid intracellular vaccine (HDCV) was studied in areas where it was available. Because of the high cost and initial short supply, intradermal injections of 0.1 ml HDCV were given. 567 of 570 persons achieved adequate titres. No systemic reactions were reported with intradermal HDCV.     

Rabies pre-exposure prophylaxis using intradermal human diploid cell vaccine: immunologic efficacy and cost-effectiveness in a university medical center and a review of selected literature

The authors studied the antigenicity of intradermal human diploid cell rabies vaccine administered to 40 laboratory workers considered to be at-risk at the University of Virginia Medical Center. A 1-year postvaccination serology was determined for 20 of those 40, all of whom demonstrated an antirabies titer greater than or equal to 1:50 by the raped fluorescent focus inhibition test. By 2 years' postvaccination, 5 of 40 subjects had "unprotective levels" (less than 1:5), whereas 35 had titers greater than or equal to 1:5, and none had a titer greater than or equal to 1:50. Booster doses given to four subjects whose titers had declined produced a 1-month postvaccination antirabies titer greater than or equal to 1:50 in all cases. Vaccine administration by the intradermal rather than the intramuscular route resulted in a cost savings of $120 (U.S.) per employee. This data indicate that the intradermal administration of human diploid cell vaccine for rabies pre-exposure prophylaxis achieves an immunologic response thought to be protective while providing a substantial cost savings when compared with the intramuscular route of administration. Those who receive primary pre-exposure rabies vaccination should have serologic confirmation of immunologic protection every 2 years with a booster dose given to subjects demonstrating a titer less than 1:5.     

Rabies deaths in Pakistan: results of ineffective post-exposure treatment.

OBJECTIVES: To estimate the incidence of rabies and the effectiveness of post-exposure treatment (PET) in Pakistan. METHODS: Rabies cases admitted from July 1993 to December 1994 to a public rabies isolation hospital were analyzed. Two samples (one sample each from a separate peripheral site) of a single batch of sheep brain vaccine (SBV) were also tested for potency by the National Institute of Health (NIH) test in May 1997. RESULTS: Forty patients were admitted with a history of clinical rabies. The median age was 22 years and 55% were under 15. Thirteen (23%) victims did not receive any vaccine; the remaining 27 (67%) received SBV only, and of these, 16 (40%) received a full course of SBV. No rabies immunoglobulins (RIG) or cell culture vaccines were administered. There were frequent power blackouts and no back-up supply at the public hospital. In-house potency testing of the vaccine batch by the manufacturer was adequate, although it was not tested by the World Health Organization (WHO) recommended NIH test. Samples of SBV of the same batch collected at the peripheral sites showed no potency. Rabies incidence was estimated to range between 7.0 to 9.8 cases per million annually. CONCLUSION: A multi-sectorial approach is needed to decrease rabies incidence in Pakistan. Public and healthcare practitioner education on prompt and appropriate PET, especially the use of cost-effective cell culture intradermal regimens, is needed urgently. The NIH test should be employed for vaccine potency testing. An independent agency is needed for monitoring vaccine quality and strategies are needed for maintaining cold chain. SBV should be replaced by locally manufactured second-generation cell culture rabies vaccine. Purified equine rabies immunoglobulin (ERIG) should be manufactured locally to meet national needs. Furthermore, effective dog control strategies should be implemented to decrease the rabies reservoir.     

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。     

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)     

Rabies in Thailand: 1990

Of the more than 100,000 courses of postexposure rabies treatment given in Thailand annually, 95% consist of brain tissue-derived vaccine without immune globulin. Rabies tissue culture vaccines and immune globulins are expensive by the standards of developing countries. When they are given according to either of two proven intradermal postexposure schedules, significant savings can be achieved without loss of efficacy. Purified equine rabies immune globulins account for approximately 10% of the cost of human products administered to exposed individuals and have been shown to be safe and effective. A canine preexposure immunogenicity study with a potent, inactivated tissue culture vaccine revealed that 12.5% of Thai dogs failed to develop protective antibody titers 2 months after one subcutaneous injection. Previous studies have shown significant antigenic differences between Thai street rabies virus and European and North African strains.     

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.     

Low-dose intradermal and intramuscular vaccination against hepatitis B.

Hepatitis B and its sequelae are global problems preventable by immunization. Expense limits the use of hepatitis B vaccines, but low-dose intradermal immunization has been evaluated as a cost-saving strategy in numerous studies. With few exceptions, low-dose intradermal plasma-derived vaccines have elicited protective levels of antibody in 82%-100% of young healthy adults--a proportion similar to that noted with full-dose regimens; peak levels of antibody to hepatitis B surface antigen (HBsAg) are lower with reduced doses, however. Although children respond well to low-dose intradermal immunization, this procedure is technically difficult in neonates and should not be used for those born to HBsAg-positive mothers. For persons at high risk, antibody to HBsAg must be assessed after immunization to determine the need for a booster dose. A fourth dose 1-2 years after the initial series substantially increases antibody concentrations. In low intradermal doses, recombinant vaccine elicits lower rates of seroconversion than plasma-derived vaccine. However, low intramuscular doses of recombinant vaccine give favorable results. In short, low-dose intradermal or intramuscular immunization offers protection against hepatitis B at significant savings and may be useful for mass immunization of populations at high risk.     

Rabies preexposure prophylaxis with human diploid cell rabies vaccine: a dose-response study

Recent studies suggest that human diploid cell rabies vaccine (HDCV) may not always produce acceptable titers after intradermal (id) preexposure prophylaxis. To stimulate accidental deviation from the recommended route of administration and to determine the immunogenicity of smaller-than-recommended doses of HDCV, we injected each of 154 persons either intramuscularly (im) with 100%, 10%, or 3% of the standard im dose of vaccine or id with 10%, 3% or 1% of the standard im dose. Seroconversion (titers of antibody greater than or equal to 1:11) was found in all subjects at 49 and 90 days after vaccination. Titers were higher for subjects receiving 100% of the recommended dose im than for those receiving 10% of this dose id (P less than .01); these titers in turn were higher than those from persons receiving smaller doses (P less than .05). Persons receiving 10% or 3% of the standard im dose had lower titers on day 49 than did those receiving the same dose id (P less than .05).