Two-year comparative trial on the immunogenicity and adverse effects of purified chick embryo cell rabies vaccine for pre-exposure immunization

Active safety surveillance of rabies monoclonal antibody and rabies vaccine in patients with category III potential rabies exposure

Background

A vero cell-based inactivated Rabies Vaccine (Rabivax-S) and Rabies Human Monoclonal Antibody (Rabishield) have been approved since 2016. A post-marketing surveillance was conducted in India from 2020 to 2021 to gather real world safety data on Rabivax-S and Rabishield.

Methods

This was non-interventional active surveillance in patients with category III potential rabies exposure who were administered a post-exposure prophylaxis (PEP) regimen (Rabishield and Rabivax-S) by their healthcare providers (HCPs) as per the dosages and regimens mentioned in the package insert approved by the Indian regulators. The approved schedule for PEP was local infiltration of Rabishield on Day 0 and five doses of Rabivax-S on Day 0, 3, 7, 14, and 28 (Intramuscular route, IM) or four doses of Rabivax-S on Day 0, 3, 7, and 28 (Intradermal route, ID). The primary objective of this surveillance was to generate real-world evidence on the safety and tolerability of Rabishield and Rabivax-S. All patients enrolled in the surveillance were required to report any adverse events (AEs) occurring up to Day 31 after initiation of PEP (administration of Rabishield and the first dose of Rabivax-S) to their HCP.

Findings

A total of 1000 patients with category III potential rabies exposure were enrolled across India. 991 patients received the PEP regimen with IM Rabivax-S while 9 received a PEP regimen with the ID regimen. While 32% of the patients were <12 years of age, 11.8% were ≥12 to <18 years of age and 56.2% were ≥18 years of age. The entire PEP regimen was completed by 97.3% of the enrolled patients. A total of 69 AEs were reported in 64 patients. Out of these, 49 AEs in 47 patients were assessed as causally related to the study products (26 with Rabishield and 23 with Rabivax-S). The majority of the AEs were mild and all recovered without any sequelae. One serious adverse event (SAE) of fracture of the hand was reported which was not related to either Rabishield or Rabivax-S. No case of rabies was reported.

Interpretation

Rabishield and Rabivax-S have an excellent safety profile and are well tolerated. No participant developed rabies during 31 day follow up.

Funding

The PMS was funded by Serum institute of India Private Limited which is the manufacturer of the study products.

Challenges of Rabies Serology: Defining Context of Interpretation

The case fatality rate of rabies, nearly 100%, is one of the most unique characteristic of this ancient virus infection. The crucial role rabies virus neutralizing antibody plays in protection is both well established and explanation of why rabies serology is important. Various laboratory methods can and have been used but serum neutralization methods have long been the gold standard due to the ability to measure function (neutralization), however these methods can be difficult to perform for several reasons. Assays such as enzyme linked absorbance assays (ELISA), indirect fluorescence antibody (IFA) and more recently lateral flow methods are in use. Interpretation of results can be problematic, not only between methods but also due to modifications of the same method that can lead to misinterpretations. A common assumption in review of laboratory test results is that different methods for the same component produce comparable results under all conditions or circumstances. Assumptions and misinterpretations provide the potential for detrimental decisions, ranging from regulatory to clinically related, and most importantly what ‘level’ is protective. Review of the common challenges in performance and interpretation of rabies serology and specific examples illuminate critical issues to consider when reviewing and applying results of rabies serological testing.

Serologic Response of 2 Versus 3 Doses and Intradermal Versus Intramuscular Administration of a Licensed Rabies Vaccine for Preexposure Prophylaxis

BACKGROUND

The World Health Organization recommends intradermal (ID) administration of rabies vaccine for preexposure prophylaxis.

METHODS

In a randomized trial in adults assigned to 1 of 6 treatment groups (ID vs intramuscular [IM], 2 vs 3 doses, and controls), rabies neutralizing antibody titers were measured to 1 year postvaccination.

RESULTS

ID vaccination produced acceptable antibody levels in all subjects (2- and 3-dose groups). At day 365, acceptable levels were 40% for IM and 50% for ID 2-dose schedule, and 70% for IM and 60% for ID 3-dose schedule.

CONCLUSIONS

ID rabies vaccination induces acceptable antibody titers at a fraction of the dose.

CLINICAL TRIALS REGISTRATION

NCT02374814.

Fractional dose of intradermal compared to intramuscular and subcutaneous vaccination - A systematic review and meta-analysis

BACKGROUND

Vaccine supply shortages are of global concern. We hypothesise that intradermal (ID) immunisation as an alternative to standard routes might augment vaccine supply utilisation without loss of vaccine immunogenicity and efficacy.

METHODS

We conducted a systematic review and meta-analysis searching Medline, Embase and Web of Science databases. Studies were included if: licensed, currently available vaccines were used; fractional dose of ID was compared to IM or SC immunisation; primary immunisation schedules were evaluated; immunogenicity, safety data and/or cost were reported. We calculated risk differences (RD). Studies were included in meta-analysis if: a pre-defined immune correlate of protection was assessed; WHO-recommend schedules and antigen doses were used in the control group; the same schedule was applied to both ID and control groups (PROSPERO registration no. CRD42020151725).

RESULTS

The primary search yielded 5,873 articles, of which 156 articles were included; covering 12 vaccines. Non-inferiority of immunogenicity with 20-60% of antigen used with ID vaccines was demonstrated for influenza (H1N1: RD -0·01; 95% CI -0·02, 0·01; I² = 55%, H2N3: RD 0·00; 95% CI -0·01, 0·01; I² = 0%, B: RD -0·00; 95% CI -0·02, 0·01; I² = 72%), rabies (RD 0·00; 95% CI -0·02, 0·02; I² = 0%), and hepatitis B vaccines (RD -0·01; 95% CI -0·04, 0·02; I² = 20%). Clinical trials on the remaining vaccines yielded promising results, but are scarce.

CONCLUSIONS

There is potential for inoculum/antigen dose-reduction by using ID immunisation as compared to standard routes of administration for some vaccines (e.g. influenza, rabies). When suitable, vaccine trials should include an ID arm.

Rabies Antibody Response After Booster Immunization: A Systematic Review and Meta-analysis

Although fatal once symptomatic, rabies is preventable by administration of pre- and post-exposure vaccines. International guidelines suggest lifelong protection by a pre-exposure vaccination scheme followed by timely post-exposure vaccines. Rapidity and magnitude of the antibody recall response after booster inoculation are essential, as many people have been previously immunized a long time ago. The objective of this study was therefore to systematically review the evidence on the boostability of rabies immunization to date. We included 36 studies, of which 19 studies were suitable for meta-analysis. Reduced antibody levels were found after intradermal primary schedules as compared to intramuscular schedules. However, responses after booster immunization were adequate for both routes. Although studies showed that antibody levels decline over time, adequate booster responses were still retained over long time intervals indicating that post-exposure treatment is effective without extra measures after long periods of time.

A single center, open label study of intradermal administration of an inactivated purified chick embryo cell culture rabies virus vaccine in adults

In the USA, rabies vaccines (RVs) are licensed for intramuscular (IM) use only, although RVs are licensed for use by the intradermal (ID) route in many other countries. Recent limitations in supplies of RV in the USA reopened discussions on the more efficient use of available biologics, including utilization of more stringent risk assessments, and potential ID RV administration. A clinical trial was designed to compare the immunogenic and adverse effects of a purified chicken embryo cell (PCEC) RV administered ID or IM. Enrollment was designed in four arms, ID Pre-Exposure Prophylaxis (Pre-EP), IM Pre-EP, ID Booster, and IM Booster vaccination. Enrollment included 130 adult volunteers. The arms with IM administration received vaccine according to the current ACIP recommendations: Pre-EP, three 1mL (2.5 I.U.) RV doses, each on day 0, 7, and 21; or a routine Booster, one 1ml dose. The ID groups received the same schedule, but doses administered were in a volume of 0.1mL (0.25 I.U.). The rate of increase in rabies virus neutralizing antibody titers 14-21days after vaccination were similar in the ID and correspondent IM groups. The GMT values for ID vaccination were slightly lower than those for IM vaccination, for both naïve and booster groups, and these differences were statistically significant by t-test. Fourteen days after completing vaccination, all individuals developed RV neutralizing antibody titers over the minimum arbitrary value obtained with the rapid fluorescent focus inhibition test (RFFIT). Antibodies were over the set threshold until the end of the trial, 160days after completed vaccination. No serious adverse reactions were reported. Most frequent adverse reactions were erythema, induration and tenderness, localized at the site of injection. Multi use of 1mL rabies vaccine vials for ID doses of 0.1 was demonstrated to be both safe and inmunogenic.

Alum adjuvanted rabies DNA vaccine confers 80% protection against lethal 50 LD50 rabies challenge virus standard strain

Rabies is a serious concern world-wide. Despite availability of rabies vaccines for long; their efficacy, safety, availability and cost effectiveness has been a tremendous issue. This calls for improvement of rabies vaccination strategies. DNA vaccination has immense potential in this regard. The DNA vaccine pgp.LAMP-1 conferred 60% protection to BALB/c mice against 20 LD₅₀ rabies challenge virus standard (CVS) strain challenge. Upon supplementation with Emulsigen-D, the vaccine formulation conferred complete protection against lethal challenge. To assess the feasibility of this vaccine formulation for human use, it was tested along with other FDA approved adjuvants, namely, Alum, Immuvac, Montanide ISA720 VG. Enhanced immune response correlated with high IgG antibody titer, Th2 biased response with a high level of rabies virus neutralizing antibodies (RVNAs) and IgG1/IgG2a ratio >1, observed upon alum supplementation of the rabies DNA vaccine. The total IgG antibody titer was 2IU/ml and total RVNA titer was observed to be 4IU/ml which is eight times higher than the minimum protective titer recommended by WHO. Furthermore, it conferred 80% protection against challenge with 50 LD₅₀ of the rabies CVS strain, conducted in compliance with the potency test for rabies recommended by the National Institutes of Health (NIH), USA. Previously, we have established pre-clinical safety of this vaccine as per the guidelines of Schedule Y, FDA as well as The European Agency for evaluation of Medicinal Products. The vaccine showed no observable toxicity at the site of injection as well as at systemic level in Wistar rats when administered with 10X recommended dose. Therefore, supplementation of rabies DNA vaccine, pgp.LAMP-1 with alum would lead to development of a non-toxic, efficacious, stable and affordable vaccine that can be used to combat high numbers of fatal rabies infections tormenting developing countries.

Infectious and noninfectious triggers in Guillain-Barré syndrome

Guillain-Barré syndrome (GBS) is the commonest cause of acquired flaccid paralysis in the world and regarded by many as the prototype for postinfectious autoimmunity. Here the authors consider both infectious and noninfectious triggers of GBS and determine where possible what immunological mechanisms may account for this association. In approximately two-thirds of cases, an infectious trigger is reported in the weeks that lead up to disease onset, indicating that the host's response to infection must play an important role in disease pathogenesis. The most frequently identified bacteria, Campylobacter jejuni, through a process known as molecular mimicry, has been shown to induce cross-reactive anti-ganglioside antibodies, which can lead to the development of axonal-type GBS in some patients. Whether this paradigm can be extended to other infectious organisms or vaccines remains an important area of research and has public health implications. GBS has also been reported rarely in patients with underlying systemic diseases and immunocompromised states and although the exact mechanism is yet to be established, increased susceptibility to known infectious triggers should be considered most likely.

Review of human rabies prophylaxis and treatment

Rabies is a devastating encephalitis caused by RNA viruses that use mammals as reservoirs. In the United States, most naturally acquired human cases have come from bats. The use of appropriate preexposure and postexposure prophylaxis can be nearly 100% effective. If prophylaxis is not used, or is implemented incorrectly, the patient may develop clinical rabies, which is almost universally fatal. All health care practitioners should be familiar with the appropriate evaluation of patients presenting with a possible rabies exposure and ensure that expeditious and appropriate prophylaxis is provided to help prevent the development of this lethal disease.

The role of vaccination in rabies prevention

Rabies vaccines have evolved from the first crude nerve tissue vaccines developed by Louis Pasteur and his colleagues in 1885. Currently, safe and efficacious rabies vaccines for humans and animals are produced in several cell culture systems with 10 vaccine regimens recommended by WHO and/or ACIP for pre-exposure and post-exposure prophylaxis in humans. Rabies vaccines are a critical component in the strategy to reduce the dog rabies, the cause of 98% of all global human rabies deaths. However, eliminating rabies in the reservoir animal species is not possible without an intersectoral approach including collaboration between animal and human health experts. There is an urgent need to establish national risk assessment systems in regions where surveillance is limited to non-existent.

Immunogenicity and booster efficacy of pre-exposure rabies vaccination

A multivariate analysis was used to identify factors influencing the immunogenicity of rabies vaccine and to assess the efficacy of booster injections in a cohort of 407 people monitored prospectively for 10 years after primary vaccination. Rabies vaccine (HDCV or PVRV) was injected by intramuscular route either on days 0 and 28 or on days 0, 7 and 28. All the participants received a booster injection on day 365. At the end of follow-up (year 10), 163 subjects had titers >0.5IU/ml (group A) and 59 subjects had titers <0.5IU/ml (group B: poor responders). The number of injections had a significant influence (P<0.001) on the magnitude of the serological response to rabies vaccine, but the type of vaccine and the potency of the batches did not (P=0.07 and P=0.06, respectively). The difference between GMTs on day 365 and day 379 was significantly lower in group B than in group A (13 and 50.70IU/ml, respectively; P<0.001). In conclusion, our study confirms that the rabies pre-exposure vaccination protocol of three intramuscular injections significantly decreases the proportion of poor responders at 10 years. Moreover, our findings indicate that a routine booster injection at 1 year could significantly increase the levels and duration of antibody titers.

Human monoclonal antibody and vaccine approaches to prevent human rabies

Rabies, being a major zoonotic disease, significantly impacts global public health. It is invariably fatal once clinical signs are apparent. The majority of human rabies deaths occur in developing countries. India alone reports more than 50% of the global rabies deaths. Although it is a vaccine-preventable disease, effective rabies prevention in humans with category III bites requires the combined administration of rabies immunoglobulin (RIG) and vaccine. Cell culture rabies vaccines have become widely available in developing countries, virtually replacing the inferior and unsafe nerve tissue vaccines. Limitations inherent to the conventional RIG of either equine or human origin have prompted scientists to look for monoclonal antibody-based human RIG as an alternative. Fully human monoclonal antibodies have been found to be safer and equally efficacious than conventional RIG when tested in mice and hamsters. In this chapter, rabies epidemiology, reservoir control measures, post-exposure prophylaxis of human rabies, and combination therapy for rabies are discussed. Novel human monoclonal antibodies, their production, and the significance of plants as expression platforms are emphasized.

Pre-exposure rabies vaccination using purified chick embryo cell rabies vaccine intradermally is immunogenic and safe

OBJECTIVE

To demonstrate the safety and immunogenicity of intradermal rabies pre-exposure prophylaxis with purified chick embryo cell vaccine (PCECV) in schoolchildren age 5 to 8 years in Thailand.

STUDY DESIGN

In a randomized, open-label, phase II clinical trial, 2 or 3 intradermal doses of 0.1 mL PCECV (Rabipur) were administered to 703 schoolchildren on days 0 and 28 or on days 0, 7, and 28. In 206 children, 2 simulated post-exposure booster doses were given 1 year after the primary vaccination series. Rabies virus- neutralizing antibody (RVNA) titers were determined by the rapid fluorescent focus inhibition test.

RESULTS

In school-age children in Thailand, a pre-exposure immunization regimen of 3 intradermal doses of PCECV produced adequate immune responses. After primary vaccination, all subjects developed RVNA titers > or =0.5 IU/mL and demonstrated a rapid increase in RVNA titer after 2 simulated post-exposure booster immunizations 1 year after the primary vaccination series. No serious adverse drug reactions occurred.

CONCLUSIONS

Rabies pre-exposure immunization with PCECV is safe and immunogenic, and its implementation could save the lives of many children in rabies-endemic areas.

Adverse Effects of Rabies Pre- and Postexposure Prophylaxis in 290 Health-Care-Workers Exposed to a Rabies Infected Organ Donor or Transplant Recipients

The recent unfortunate rabies transmissions through solid organ transplants of an infected donor in Germany required the initiation of a vaccination program to protect health care workers (HCWs) with close contact to rabies-infected patients. A systematic follow-up of adverse effects was initiated. Rabies postexposure prophylaxis (PEP) was started in 269 HCWs at four German hospitals. Pre-exposure prophylaxis (PreEP) was administered to 74 HCWs caring for an already diagnosed rabies patient. At each vaccination date, HCWs were interviewed for symptoms possibly representing adverse effects. Adverse effects of PEP and PrePEP were compared. Out of 269 HCWs, 216 were included for the investigation of adverse effects. Of these 216 HCWs, 114 (53%) individuals developed at least one systemic adverse effect. Incidences of tiredness (30.6%), malaise (26.4%), headache (26.9%), dizziness (14.8%), and chills (13.0%) declined in the course of PEP (p < 0.05), whereas incidences of fever (7.4%), paraesthesias (7.9%), arthralgias (1.9%), myalgias (4.2%), nausea (9.3%), diarrheas (2.8%) and vomiting (1.4%) did not. In 11 (5.1%) HCWs PEP was discontinued mostly due to adverse reactions (four suffered strong headaches, two HCWs meningeal irritations, two chills, one paraesthesia, one malaise, and one a rush). Systemic effects of PEP or PreEP did not differ significantly. Despite relatively high incidences of moderate severe adverse reactions rabies PEP is safe. Strong headache, tiredness, dizziness, and paraesthesias are the most important postvaccinal symptoms. Vaccinees suffering from adverse effects of PEP must be strongly encouraged to complete PEP, as it is to date the only protection against fatal rabies.

Safety review of the purified chick embryo cell rabies vaccine: Data from the Vaccine Adverse Event Reporting System (VAERS), 1997–2005

On October 20, 1997, the U.S. Food and Drug Administration (FDA) licensed Purified Chick Embryo Cell (PCEC, RabAvert) vaccine against rabies in humans following clinical trials demonstrating safety and efficacy. From October 1997 through December 2005, the Vaccine Adverse Event Reporting System (VAERS) received 336 reports of adverse events (AEs) following vaccination with PCEC vaccine in the U.S.; there were no death reports. Serious events, including 20 hospitalizations and 13 neurological events, were described in 24 (7%) reports. There was no pattern among the 13 neurological AEs suggesting a plausible relationship to vaccination. A total of 20 AEs, 3 serious, were classified as possible anaphylaxis. There were 312 non-serious AEs (93%). Nineteen reports (6%) described that the vaccination series was discontinued because of non-serious AEs. Most reported AEs are non-serious and consistent with pre-licensure safety data. The rabies risk must be carefully considered before vaccine discontinuation.

Risk of rabies infection and adverse effects of postexposure prophylaxis in healthcare workers and other patient contacts exposed to a rabies virus-infected lung transplant recipient

BACKGROUND

Rabies virus was inadvertently transmitted to a lung transplant recipient through donor lungs. The patient was given ventilatory assistance and cared for postoperatively for 6 weeks before a diagnosis of rabies virus infection was made. Postexposure prophylaxis (PEP) was offered to potentially exposed healthcare workers (HCWs).

METHODS

Only HCWs classified as belonging to possible and/or proven contact groups (according to a standardized interview) received PEP. The risk of individual HCWs being exposed to rabies virus was reassessed on the basis of viral concentrations measured in the patient's excretions and body fluids. HCWs who were vaccinated as part of PEP were followed up prospectively according to a standardized procedure.

RESULTS

Of 179 HCWs and other patient contacts, 132 met the eligibility criteria for PEP (118 [89.4%] with possible contact and 14 [10.6%] with proven contact with the patient's excretions and/or body fluids). One hundred thirty-one individuals started PEP, and 126 met the inclusion criteria for analysis. Of these, 48 (38%) developed at least 1 adverse effect (8 [6.3%] had fever, 37 [29.4%] had headache, 3 [2.4%] had lymphadenopathy, 17 [13.5%] had dizziness, and 6 [4.8%] had paresthesia). No HCW or other patient contact developed rabies or serious PEP-related adverse effects. Reassessment of the individual's risk of infection as a function of the viral concentration in the patient's excretions and/or body fluids (up to 5.12 x 10(7) copies/mL) revealed that 103 HCWs (78.0%) had contact with high-risk substances (89 [67.40%] had possible contact and 14 [10.7%] had proven contact).

CONCLUSION

HCWs can be exposed to significant viral concentrations in excretions and/or body fluids from rabies virus-infected lung transplant recipients. Because widespread use of PEP entails the possibility of significant health problems for HCWs considered to be at risk of contracting rabies, applying a rational indication for PEP is crucial.

An immunogenicity study of a newly introduced purified vero cell rabies vaccine (Abhayrab) manufactured in India

Purified Vero cell culture rabies vaccine "Abhayrab" manufactured by Human Biologicals Institute, Ooty, India was subjected for immunogenicity studies. Pre-exposure study was undertaken on 60 healthy volunteers (Group I) with vaccination on days 0, 7 and 21. A group of 75 patients of category II (Group II), 67 of category III (Group III) were given post-exposure prophylaxis and 88 patients of category III were administered with rabies immunoglobulins (Group IV) along with post-exposure prophylaxis as per World Health Organization (WHO) recommendations with a booster on day 90. The volunteers and patients vaccinated showed very few adverse side effects. The blood samples collected from volunteers (Group I) on days 14, 35 and 365 and patients (Group II-IV) on days 14, 30, 90 and 365 showed geometric mean titres (GMT) of >0.5 IU/ml. The study indicated new rabies vaccine manufactured in India was found to be safe and immunogenic.

A review of licensed viral vaccines, some of their safety concerns, and the advances in the development of investigational viral vaccines

Viral vaccines could be considered among the most important medical achievements of the 20th century. They have prevented much suffering and saved many lives. Although some curative antiviral drugs exist, we desperately depend on efforts by academic, governmental and industrial scientists in the advancement of viral vaccines in the prevention and control of infectious diseases. In the next decade, we hope to see advancement in the development of current and investigational viral vaccines against childhood and adult infections. In this article, we will review the licensed viral vaccines, some of their safety concerns, and the advances in the development of investigational viral vaccines.

Rabies: recent developments

Rabies remains as one of the most feared zoonotic diseases in the world. All warm-blooded animals are susceptible to infection by the virus, but the main vectors of human infection are dogs and cats. The control of rabies largely depends on the prevention of infection of dogs and cats by vaccination in endemic areas and the control of their movement, including measures of quarantine and vaccination, in rabies-free countries. This paper provides an overview on recent developments in rabies, with particular emphasis on the epidemiology, pathogenesis, diagnosis, and control.

Rabies vaccines: from the past to the 21st century

Since the first development of a rabies vaccine by Pasteur in the late 19th century, second- and third-generation vaccines with improved efficacy and less reactogenicity have been developed for use in humans and animals. Despite the availability of safe but rather expensive vaccines based on inactivated virus propagated in diploid cell cultures, much of the human vaccinations worldwide are still carried out with nerve tissue-containing vaccines, which have various side effects. A number of experimental vaccines are under development that may provide alternative safe and potent but less expensive vaccine options. These include DNA vaccines, recombinant viral vaccines, and recombinant protein vaccines. Further testing is needed to determine if and which one of these novel vaccines will make their way into mass production and application in the future.

Active immunization in the United States: developments over the past decade

The Centers for Disease Control and Prevention has identified immunization as the most important public health advance of the 20th century. The purpose of this article is to review the changes that have taken place in active immunization in the United States over the past decade. Since 1990, new vaccines have become available to prevent five infectious diseases: varicella, rotavirus, hepatitis A, Lyme disease, and Japanese encephalitis virus infection. Improved vaccines have been developed to prevent Haemophilus influenzae type b, pneumococcus, pertussis, rabies, and typhoid infections. Immunization strategies for the prevention of hepatitis B, measles, meningococcal infections, and poliomyelitis have changed as a result of the changing epidemiology of these diseases. Combination vaccines are being developed to facilitate the delivery of multiple antigens, and improved vaccines are under development for cholera, influenza, and meningococcal disease. Major advances in molecular biology have enabled scientists to devise new approaches to the development of vaccines against diseases ranging from respiratory viral to enteric bacterial infections that continue to plague the world's population.

Pre-exposure rabies vaccination: strategies and cost-minimization study

An alternative strategy for pre-exposure rabies vaccination to the institutional recommendations of the World Health Organization and the Centers for Disease Control and Prevention is proposed based on recent long-term follow-up of post-vaccinal seroconversion rates. The alternative strategy uses the same primary series (i.e. vaccination in the deltoid area on D0, D7, and D28), but is completed by a scheduled booster vaccination at D365. The frequency of recommended subsequent booster injections depends on the serological test results obtained by a RFFIT on D379 and 3 years later. The objective of this study was to compare the efficiency of the two pre-exposure strategies. A cost-minimization analysis was carried out to compare the two rabies pre-exposure vaccination and serological test strategies based on the data from two published studies on the long-term evolution of the immunity achieved using the different recommendations. For a theoretically equivalent immunogenicity, the cost of the alternative strategy ranged from 1.7 to 5.2 times lower than that of the institutional recommendations. A sensitivity analysis confirmed the robustness of the results. The alternative strategy should be validated externally under field conditions. This approach would compare its real efficiency to the institutional recommendations.

Immunization for children traveling abroad

More children are travelling these days, often to underdeveloped countries with high prevalence of vaccine-preventable vector-borne, food-borne, zoonotic, and other infections. The pretravel office visit involves consideration of routine and travel vaccines. Epidemiology of typhoid fever, rabies, yellow fever, Japanese encephalitis, vaccines against them, and their recommended use are reviewed.

Persistence of humoral immunity to rabies 1100 days after immunization and effect of a single booster dose of rabies vaccine

Forty-four vaccinees immunized with rabies vaccine and human rabies immunoglobulin according to the abbreviated intramuscular regimen (the 2-1-1 schedule) were followed-up after 1100 days and had their blood samples taken. The persistence of rabies neutralizing antibody was proven in the sera of all vaccinees. 56% of whom demonstrated titres > or = 0.5 IU ml-1. At the same day the vaccinees were given a single booster dose of vaccine whose effect was measured 2 weeks later. With the RFFI test on day 1114, sera revealed an extraordinarily high booster response in all 44 vaccinees. The study proved the anamnestic response after a full course of rabies vaccination to be a very stable one, and the capability of a single booster dose of vaccine to evoke high-titred rabies antibody response. Of the four vaccines used in the study, under comparable conditions HDCV proved superior to PCECV PDEV and PVRV on all 3 days of serology-35, 1100 and 1114, though this difference was statistically attested only on days 35 and 1114.

A global review of rabies vaccines for human use

Rabies is one of the oldest known diseases of mankind, yet it has been only slightly more than 100 years since Pasteur developed the first vaccine for post-exposure treatment. Since this first crude nerve tissue vaccine, numerous other rabies vaccines for human use have been developed and used with varying degrees of effectiveness and safety. When used appropriately, new cell culture vaccines provide nearly 100% protection with a high degree of safety: yet over 40,000 people world-wide die from rabies each year. Several pre- and post-exposure controlled vaccine trials and clinical studies have shown that the purified chick embryo cell (PCEC) vaccine, Rabipur, is as safe and effective as the rabies human diploid cell vaccine (HDCV), which is currently considered the gold standard. Additionally, PCEC vaccine does not result in immune-mediated hypersensitivity reactions following booster doses seen in about 6% of those receiving HDCV boosters following an initial series of HDCV.

Safety and immunogenicity of Lyssavac Berna human diploid cell rabies vaccine in healthy adults

A clinical trial testing the safety and immunogenicity of a newly developed human diploid cell rabies vaccine (Lyssavac-HDC) was conducted on subjects at three colleges of veterinary medicine in the United States. Lyssavac-HDC is a sterile lyophilized vaccine containing no antibiotics or preservatives and is administered intramuscularly as a 0.5 ml dose of vaccine containing at least 2.5 i.u. of rabies inactivated antigen per dose. Subjects were given either a three dose pre-exposure series (days 0, 7, and 28), followed by one booster dose of vaccine (day 360); or a five dose simulated post-exposure series of injections (days 0, 3, 7, 14, and 28). All subjects in the post-exposure and pre-exposure groups possessed adequate levels of rabies neutralizing antibody (> or = 5) when tested on day 14 and day 28, respectively. Subjects in the pre-exposure group demonstrated a vigorous anamnestic response after the administration of one booster dose of vaccine on day 360. The type and severity of local and systemic reactions observed were comparable to other primary cell culture rabies vaccines. Significantly, there were no type III hypersensitivity reactions reported in subjects previously immunized with Lyssavac-HDC after the administration of a booster dose of vaccine on day 360.

Effect of one booster dose in antirabies vaccination

The antibody response obtained after one booster dose of rabies vaccine prepared in suckling mice brains at Serviço de Saúde Pública da Cidade do Rio de Janeiro is described. Four prime vaccinal groups were used: group I, persons who had received 16 doses 10 years before this investigation; group II, persons who had received 5 doses of the vaccine 10 years before; group III, persons who had received 9 doses 5 years before; and group IV, persons who had received 16 doses 5 years before. One booster dose of the vaccine was administered to all persons involved in the study. Blood samples were collected before vaccination (day 0), then 7 and 30 days after vaccination. Antibody titres were determined by seroneutralization test in mice (SWM). The results demonstrated that all persons who had been treated with 5, 9 or 16 doses of the vaccine 5 to 10 years before had their antibody titres increased on the 7th and 30th days after one booster dose.

Longevity of rabies antibody titre in recipients of human diploid cell rabies vaccine

Sera from individuals across the USA and Peace Corps Volunteers (PCV) were assayed for neutralizing antibody to human diploid cell rabies vaccine (HDCV). A pairwise comparison between intramuscular (i.m.) and intradermal (i.d.) administration, PCV and non-PCV, revealed statistically significant differences between i.m. and i.d. for PCV and non-PCV, and between PCV and non-PCV for i.d. and i.m. administration. Survival analysis and frequency tables employing chi 2 tests determined that the percentage probability of maintaining an adequate titre from 1.5-2.0 years after primary vaccination was 99% in non-PCV i.m., 93% in non-PCV i.d., 88% in PCV i.m., and 64% in PCV i.d.