EDQM biological reference preparation for rabies vaccine (inactivated) for veterinary use

Rabies is a deadly zoonotic disease. Control of rabies in animals by vaccination is an important strategy to protect humans from infection and control the spread of the disease. Requirements for the quality control of rabies vaccines (inactivated) for veterinary use include an in vivo quantitative potency determination as outlined in the Ph. Eur. monograph 0451. Performance of this assay requires a reference preparation calibrated in International Units (IU). A European Pharmacopeia (Ph. Eur.) Biological Reference Preparation (BRP) for rabies vaccines (inactivated) for veterinary use, calibrated in IU, has been established for this purpose. Due to the dwindling stocks of the current batch (batch 4) of Ph. Eur. BRP for rabies vaccines (inactivated) for veterinary use, a collaborative study was run as part of the EDQM Biological Standardisation Programme to establish BRP batch 5. Ten laboratories, including Official Medicines Control Laboratories and manufacturers, participated. The candidate BRP5 was assayed against the 6(th) International Standard for rabies vaccine using the in vivo vaccination-challenge assay (monograph 0451) to assign a potency value. The candidate was also compared to BRP batch 4 to establish continuity. Taking into account the results from the comparisons a potency of 10 IU/vial was assigned and in March 2015 the Ph. Eur. Commission adopted the material as Ph. Eur. BRP for rabies vaccines (inactivated) for veterinary use batch 5. In addition to the in vivo assay 3 laboratories tested the candidate material using their in-house in vitro assays for information.

Twenty year experience of the oral rabies vaccine SAG2 in wildlife: a global review

The SAG2 vaccine (RABIGEN® SAG2) is a modified live attenuated rabies virus vaccine, selected from the SAD Bern strain in a two-step process of amino acid mutation using neutralizing monoclonal antibodies. The strain is genetically stable and does not spread in vivo or induce a persistent infection. Its absence of residual pathogenicity was extensively demonstrated in multiple target and non target species (such as wild carnivores and rodent species), including non-human primates. The efficacy of SAG2 baits was demonstrated according to the EU requirements for the red fox and raccoon dog. The use of safe and potent rabies vaccines such as SAG2 largely contributed to the elimination of rabies in Estonia, France, Italy and Switzerland. Importantly, these countries were declared free of rabies after few years of oral vaccination campaigns with SAG2 baits distributed with an appropriate strategy. The excellent tolerance of the SAG2 vaccine has been confirmed in the field since its first use in 1993. No safety issues have been reported, and in particular no vaccine-induced rabies cases were diagnosed, after the distribution of more than 20 million SAG2 baits in Europe.

A semi-quantitative serological method to assess the potency of inactivated rabies vaccine for veterinary use

Potency is one of the most important indexes of inactivated vaccines. A number of methods have been established to assay the potency, of which the NIH test and single-dose mouse protection test are the "prescribed methods". Here, we report a method to semi-quantitatively assay the potency of an inactivated rabies vaccine, which uses fewer animals and takes less time to complete. Depending on the quality requirements of a vaccine (e.g. minimum potency), a rabies reference vaccine is, for example, diluted to the minimum potency, and 50 μL of the dilution is taken to inoculate 10 mice. The same amount of the test rabies vaccine is inoculated into another 10 mice. After two weeks, all mice are bled and serum samples are assayed for viral neutralizing antibody by the fluorescent antibody virus neutralization (FAVN) test. By comparing the median and interquartile range of antibody titers of the reference vaccine with those of the test vaccine, the test vaccine potency can be semi-quantitatively judged as to whether it is in accord with the required quality. The reliability of this method was also confirmed in dogs. The procedure can be recommended for batch potency testing during inactivated rabies vaccine production.

Potency testing of veterinary rabies vaccines: replacement of challenge by in vitro testing: considerations for development of alternative assays

Vaccination of domestic animals against rabies creates a critical barrier between wildlife reservoirs and the human population. Ensuring these vaccines are potent and effective is paramount in preventing human exposure to this deadly and costly disease. The National Institutes of Health (NIH) test is, at present, the most widely used and internationally recommended potency assay for batch testing inactivated rabies vaccines. This test has numerous inherent limitations and disadvantages, including a lack of precision. The NIH test requires a large number of animals and involves unrelieved pain and suffering. A relevant in vitro assay should provide a more accurate, reproducible, rapid, safe, and humane rabies vaccine potency test.

Collaborative study for validation of a serological potency assay for rabies vaccine (inactivated) for veterinary use

European Pharmacopoeia (Ph. Eur.) monograph 0451 on Rabies vaccine (inactivated) for veterinary use describes an in vivo batch potency test that is based on the NIH test. This assay uses a large number of mice and results in a significant degree of suffering. In the interest of replacement, reduction and refinement of animal tests (3R) a serological potency assay for Rabies vaccine (inactivated) for animal use, developed and validated at the Paul-Ehrlich-Institut, has been assessed in a collaborative study organised by the EDQM (European Directorate for the Quality of Medicines & HealthCare). The goal was to demonstrate the wider transferability of the proposed assay and confirm its suitability. The study involved 13 laboratories and assessed 4 different vaccines from the EU market. Results of the study confirm that a limit test using a relatively small number of animals in a serological assay is possible, reproducible and reliable. The optimal number of animals per vaccine is product specific but may roughly be indicated to be between 8 and 10 for the products included in this study. Non-responders should be included in the analysis because they may reflect sub-potent vaccines. However, there may be a need to impose a maximum on the number of non-responders allowed for the reference vaccine as a monitor for assay validity. This assay provides a significant 3R improvement in terms of both the number of animals used and the amount of suffering entailed and provides a more reliable and reproducible assay format than the vaccination challenge assay. It also reduces the time required as compared to the vaccination challenge assay. It has been recommended to the Ph. Eur. group of experts 15V that this assay be included as an alternative to the batch potency assay in the Ph. Eur. monograph 0451.

Immunogenicity of the ERA G 333 rabies virus strain in foxes and raccoon dogs

The immunogenic properties of ERA G 333 attenuated rabies virus strain in foxes and raccoon dogs by the oral route of administration were examined. This strain is a proposed candidate for oral rabies vaccine in Russia. As was previously demonstrated, the advantage of this virus, provided by the US Centers for Disease Control and Prevention in the framework of the Biotechnology Engagement Program, is apathogenicity for 3-week old and adult mice, as well as for other target and non-target species, even when challenged via the intracerebral route. A group of 12, 7-8 month-old foxes and eight wild captured raccoon dogs were given 2.0 ml of ERA G 333 (titre 107.5 FFU) orally on the tongue. Another three foxes and three raccoon dogs were retained as controls. Blood samples were collected before immunization and on day 60 thereafter. The antibody titres were determined by the fluorescent antibody virus neutralization (FAVN) test. Eight foxes and three raccoon dogs showed seroconversion on day 60 postvaccination. Eleven foxes and four raccoon dogs survived challenge with a virulent rabies virus strain. This study has demonstrated the possibility of using ERA G 333 for the oral vaccination of red foxes and raccoon dogs. Further experiments are needed to determine the effective dose, virus stability, and the strength and duration of immunity.

Evaluation of cytokines concentration and percentage of survival of rabies virus-infected mice submitted to anti-rabies Vero-cell propagated vaccine and P. acnes

Previously, survival of rabies infection was shown to correlate with low IL-6 serum concentration in mice subjected to post-exposure treatment with the Fuenzalida Palacios rabies vaccine in conjunction with the immunomodulator Propionibacterium acnes, previously Corynebacterium parvum. Considering the substitution of the Fuenzalida Palacios rabies vaccine by the Vero cell raised anti-rabies vaccine in almost all countries, the objective of this work was to evaluate the survival and cytokine serum concentration of rabies virus-infected mice treated with P. acnes in conjunction with or the anti-rabies-VERO vaccine. For this, Swiss mice were experimentally infected with street rabies virus and subjected to vaccine and/or P. acnes following infection. Animals were killed at different times and serum was collected to evaluate cytokines. The greatest survival was observed in animals given one or two does of P. acnes in the absence of vaccination. Animals given anti-rabies VERO vaccine alone or with three doses of P. acnes had the second highest survival rate. The group that had the highest percentage of mortality also had the highest IL-6 concentration on the 10th day, a time correlating with clinical symptoms of the animals. The results reinforce the inefficacy of anti-rabies vaccine in only one dose as a post-exposure treatment irrespective of the type of vaccine used, the immunomodulation activity of P. acnes in rabies post-exposure treatment and suggest a role for IL-6 in rabies virus pathogenesis.

A simple immuno-capture ELISA to estimate rabies viral glycoprotein antigen in vaccine manufacture

Rabies is an endemic, fatal zoonotic disease in the developing countries. Prevention and post-exposure therapy require safe and efficacious vaccines. The vaccine potency depends on the amount of immunogenic rabies viral glycoprotein antigen in the vaccine preparation. In order to estimate the rabies viral glycoprotein antigen, a specific monoclonal antibody was developed and used in an immuno-capture ELISA (IC-ELISA). The monoclonal antibody binds a conformational epitope on the natively folded rabies viral glycoprotein as indicated by specific, membrane fluorescence on unfixed, rabies virus infected murine neuroblastoma (MNA) cells and glycoprotein gene encoding plasmid transfected COS cells. In addition, the monoclonal antibody competes with and blocks a glycoprotein antigen site III binding monoclonal antibody (mAb-D1, Institut Pasteur, Paris, France). The monoclonal antibody was used in an IC-ELISA using an in-house standard to quantify the rabies viral glycoprotein antigen in 12 vaccine preparations with potency values ranging from 4 to 18 IU. The results indicated a good correlation with the NIH mouse potency assay (r=0.83). The immuno-capture ELISA described in this study can be used to quantify the immunogenic rabies viral glycoprotein antigen in the inactivated rabies viral antigen preparation in a simple and rapid format, which enables better vaccine formulation.

Establishment of batch 4 of the Biological Reference Preparation (BRP) for rabies vaccine (inactivated) for veterinary use

9 laboratories from 7 countries including both laboratories from the public and private sector participated in a collaborative study organised under the aegis of the European Directorate for the Quality of Medicines Biological Standardisation Programme in order to establish batch 4 of the European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for rabies vaccine (inactivated) for veterinary use. Establishment of Ph. Eur. BRP batch 4 was necessary in order to replace Ph. Eur. BRP batch 3, the stocks of which were dwindling. 8 laboratories provided results. Ph. Eur. BRP batch 4 was calibrated against the 5th International Standard for inactivated rabies vaccine in International Units (IU) using the vaccination challenge method of the Ph. Eur. monograph 0451. The International Standard (IS), Ph. Eur. BRP batch 4 and batch 3 are all freeze-dried vaccines prepared by beta-propiolactone inactivation of the Pitman Moore strain of rabies. Based on the results of the study, a potency of 11 IU/vial was assigned to Ph. Eur. BRP batch 4 for rabies vaccine (inactivated) for veterinary use. Nevertheless, it was noted that the vaccination challenge assay used as the "golden standard" for potency determination of inactivated rabies vaccines for veterinary use is a crude assay requiring the use of a large number of animals. Evidence from this study and from the collaborative study to establish Ph. Eur. BRP batch 3 suggests that the assay is difficult to perform and provides highly variable results. The validation of a suitable in vitro alternative is therefore highly recommended, as is the possible improvement of the in vivo assay, which will most likely remain the "golden" standard.

Safety and immunogenicity of a new chromatographically purified rabies vaccine in comparison to the human diploid cell vaccine

BACKGROUND

Although human diploid cell vaccine (HDCV) has been available for over two decades and has a proven record of efficacy, it is very expensive to produce and can only be made in small quantities.

METHODS

In this trial, we compared the safety and immunogenicity of a new, chromatographically purified rabies vaccine (CPRV) with those of HDCV. One hundred and thirty-five healthy veterinary students were randomized in a 2:1 ratio between CPRV and HDCV respectively. Each student subsequently received an intramuscular injection of 0.5 mL of CPRV or 1mL of HDCV on days 0, 7, and 28, according to the standard preexposure regimen. Local safety data were collected for 7 days following each dose and systemic safety data for 42 days following the first dose. Vaccine administration and safety evaluation were performed by different site personnel. Sera for immunogenicity analysis were collected on days 0 (prevaccination), 28 and 42.

RESULTS

All subjects achieved an antirabies antibody titer greater than or equal to the World Health Organization (WHO) accepted threshold level of seroconversion of 0.5 IU/mL after only two of three doses of vaccine in both groups. The geometric mean titers (IU/mL) in the CPRV and HDCV groups respectively were 6.54 (range 0.50 to 64.80) and 10.22 (range 0.70 to 51.40) on day 28, and 40.51 (range 5.40 to 278.00) and 37.71 (range 5.40 to 278.00) on day 42. The percentage of subjects experiencing local reactions within 3 days after any dose ranged from 65.2% to 80.9% in the CPRV group and from 77.3% to 84.4% in the HDCV group. The local reaction reported by the greatest percentage of subjects after each dose was pain/tenderness at the injection site, and most reactions were mild. Most of the reported local reactions resolved within 0 to 3 days postvaccination. Systemic reactions decreased from 76.4% after dose 1 to 36.0% after dose 3 in the CPRV group, and similarly from 55.6% to 31.8% in the HDCV group. For all postdose periods, the systemic reaction reported by the highest percentage of subjects was myalgia. No subjects experienced an immediate local or systemic reaction.

CONCLUSIONS

In healthy adults, vaccination with CPRV using a preexposure schedule resulted in a safety and immunogenicity profile similar to that of HDCV.

[The epidemic situation of human rabies from 1984 to 2002 and its preventive measures in China]

OBJECTIVE

To summarize and analyze the epidemic situation of human rabies from 1984 to 2002 in China, and to explore the possible factors causing the increase of cases so as to provide evidence for preventive and control measures.

METHOD

National and some provincial data on the prevalence of rabies during 1984 to 2002 were collected and analyzed.

RESULTS

From 1984 to 1989, the annual reported cases were between 4 000 and 6 000 but decreased after 1990. In 1996, the reported cases decreased to the lowest level from 3 520 in 1990 to 159. However, number of reported cases has been continuously increasing since 1998 which reached 1 122 in 2002, a 7.06 times increase as compared to the number in 1996. The epidemic areas were mainly located in the southeast and southwest parts of the country, such as Sichuan, Hunan, Guangxi, Guangdong, Anhui, Fujian, etc. Furthermore, there was no significant seasonal distribution as it showed before.

CONCLUSION

Such facts as the increasing numbers of dogs, low inoculation rate to dogs, poor control on the quality of rabies vaccine, mistreatment to the wounds, and lacking good cooperation between different official departments regarding rabies control might serve as important factors responsible for the recurrence of rabies. Therefore, it is necessary to focus on the above mentioned points and to take comprehensive preventive measures to bring down the prevalence of rabies in China.

Inactivated rabies vaccine control and release: use of an ELISA method

Quality control of human rabies vaccines performed by National Control Laboratories (NCLs) prior to marketing vaccines batches requires in vivo and in vitro potency assays as requested by the relevant European Pharmacopoeia monographs, OMCLs guidelines and WHO technical recommendations. The aim of the present study was to check the suitability of an enzyme-linked immunosorbent assay (ELISA) using a virus neutralizing monoclonal antibody, directed to the rabies virus glycoprotein, to monitor the consistency of the lot to lot rabies vaccines production. Furthermore, this work was implemented to establish in house specifications for the glycoprotein content.

Thermo-stability of the oral rabies virus vaccines SAD B19 and SAD P5/88

The thermo-stability of two widely used oral rabies vaccine viruses, SAD B19 and SAD P5/88, was examined under various laboratory and field conditions. In the laboratory, both vaccine viruses were kept at 35 degrees C and titrated after 3 days. The titer of both vaccine viruses was also determined after 4 and 7 days when stored at 20 degrees C. Furthermore, vaccine baits were placed in three different micro-environments during two successive 21-day observation periods (11.9.01-2.10.01 and 2.10.01-23.10.01); (i) wooded area--location A, (ii) grassy meadow--location B, and (iii) barren soil--location C. Baits were re-collected 0, 3, 6, 9, 12, 15 and 21 days after distribution and the vaccine virus was subsequently titrated. The temperature stress for the vaccine baits was highest at location C, followed by location B and the lowest at location A. The vaccine baits were exposed to higher temperatures and higher temperature fluctuations at location B and C during trial I than during trial II. However, for both vaccines the loss of titer was more pronounced during trial II than during trial I. It is therefore suggested that under the given climatic conditions, the stability of the virus was hardly influenced by the temperatures and temperature fluctuations.

Distribution of rabies virus in infected mice, vaccinated and submitted to P. acnes as immunomodulator

The lethality and distribution of rabies virus were evaluated in swiss mice experimentally infected with street rabies virus, vaccinated and submitted to immunomodulation by P .acnes (formerly Corynebacterium parvum). The animals were sacrificed at different times,when the different tissues were collected and submitted to fluorescent antibody test (FAT) and mouse inoculation test (MIT). The group submitted to vaccination and P. acnes treatment presented a percentage of survival superior to that observed in infected mice only treated with P. acnes. Control infected animals had the lowest survival rates. The distribution of rabies virus in spleen of infected mice, vaccinated and submitted to P. acnes was superior to that verified in infected mice not treated with P.acnes. The increased survival correlated with the distribution of rabies virus in lymphoid tissues, could be interpreted as the consequence of P. acnes activity on macrophages. The results suggest the role of macrophages against rabies virus infection in mice and the importance of vaccination in the post expositive treatment of rabies.

Potency, sterility and immunogenicity of rabies tissue culture vaccine after reconstitution and refrigerated storage for 1 week

The economical Thai Red Cross intradermal (TRC-ID) post-exposure rabies treatment schedule is now widely used in Asia. However, directives from WHO and manufacturers mandated that the vaccine be used within 8h after reconstitution of the freeze-dried product. This limits the use of TRC-ID to large animal bite clinics that see several rabies exposed patients daily. This study demonstrated that refrigerated purified chick embryo and Vero cell rabies vaccines can be stored safely for up to 7 days after reconstitution; allowing use of this treatment regimen in clinics that see few rabies exposed subjects. A large project applying this method in a Northern Thai canine rabies endemic province is now in place.

Induction of protective immunity by topic application of a recombinant adenovirus expressing rabies virus glycoprotein

The objective of this study was to determine if a replication defective recombinant adenovirus expressing rabies virus glycoprotein (Adrab.gp) given through a non-invasive vaccination route (by topical application) onto the skin (NIVS) could elicit an immune response and/or protection against rabies. Groups of mice were immunized by NIVS with various doses of Adrab.gp. For comparison, groups of mice were immunized intramuscularly, subcutaneously, or intradermally with Adrab.gp. Mice received two booster immunizations at 1 and 2 months after the first immunization. Virus neutralizing antibody (VNA) titers were measured at day 21 after the first and second immunizations and at day 14 after the third immunization. Fifty percent of the mice immunized by NIVS with 2 x 10(7) and 2 x 10(8)pfu Adrab.gp vaccine developed VNA, whereas none of the control mice or the mice immunized by NIVS with the lowest dose (2 x 10(6)pfu) of Adrab.gp virus developed VNA. However, this low dose induced high titers of VNA in mice immunized by parenteral routes. Two weeks after the last immunization, all the mice were challenged with a lethal dose of rabies virus. More than 70% of the animals immunized by NIVS with > or = 2 x 10(7)pfu Adrab.gp virus survived the challenge, whereas all the mice in the negative control group and the group immunized by NIVS with the lowest dose of Adrab.gp succumbed to rabies. Taken together, the results suggest that NIVS with Adrab.gp can induce VNA production and protection against lethal challenge with rabies virus in mice.

Oral efficacy of an attenuated rabies virus vaccine in skunks and raccoons

Raccoons and skunks are major rabies reservoirs in North America. Oral vaccination is one method to consider for disease control in these carnivores. Under field conditions in the USA, only one oral rabies vaccine has been used. It is efficacious in wildlife such as raccoons (Procyon lotor), coyotes (Canis latrans), and foxes (Vulpes vulpes) but not in skunks (Mephitis mephitis). The objectives of this study were to evaluate an attenuated SAG-2 rabies virus vaccine for safety, immunogenicity, and efficacy by the oral route in skunks and raccoons. Two of five skunks and three of five raccoons developed virus neutralizing antibodies (VNA) by day 14 following oral administration of SAG-2 vaccine. All animals remained healthy. Upon challenge, naive controls succumbed to rabies. Among vaccinated animals, four of five skunks and all five raccoons had VNA on day 7 post-challenge and all survived. Given these results, SAG-2 is a promising candidate vaccine that may satisfy both safety and efficacy concerns for oral rabies immunization of major North American rabies reservoirs.

Effect of vaccination on serum concentrations of total and antigen-specific immunoglobulin E in dogs

OBJECTIVE

To determine the effect of vaccination on serum concentrations of total and antigen-specific IgE in dogs.

ANIMALS

20 female Beagles.

PROCEDURE

Groups of 5 dogs each were vaccinated repeatedly between 8 weeks and 4 years of age with a multivalent and rabies vaccine, a multivalent vaccine only, or a rabies vaccine only. A fourth group of 5 dogs served as unvaccinated controls. Serum concentrations of total immunoglobulins and antigen-specific IgE were determined following vaccination.

RESULTS

-The multivalent vaccine had little effect on serum total IgE concentrations. The concentration of IgE increased slightly following vaccination for rabies at 16 weeks and 1 year of age and increased greatly after vaccination at 2 and 3 years of age in most dogs, with a distinct variation between individual dogs. Vaccination had no effect on serum concentrations of IgA, IgG, and IgM as measured at 2 and 3 years of age. The rabies vaccine contained aluminum adjuvant in contrast to the multivalent vaccine. An increase of IgE that was reactive with vaccine antigens, including bovine serum albumin and bovine fibronectin, was detected in some of the dogs vaccinated for rabies. There was no significant correlation between serum concentrations of total IgE and antigen-specific IgE following vaccination. Serum total IgE concentration rapidly returned to preimmunization concentrations in most dogs, but high concentrations of antigen-specific IgE persisted.

CONCLUSIONS AND CLINICAL RELEVANCE

Vaccination of dogs for rabies increases serum concentrations of total IgE and induces IgE specific for vaccine antigens, including tissue culture residues. Vaccination history should be considered in the interpretation of serum total IgE concentrations.

Comparative immunogenicity and efficacy studies with oral rabies virus vaccine SAD P5/88 in raccoon dogs and red foxes

A comparative study of immunogenicity and efficacy of the oral rabies virus vaccine SAD P5/88 in raccoon dogs and foxes was conducted. The raccoon dogs received 10(6.9) (n = 6), 10(6.3) (n = 6) or 10(5.7) FFU SAD P5/88 (n = 5) by direct oral application, and subsequently all animals seroconverted. The foxes received 10(7.2) (n = 4), 10(6.2) (n = 4), 10(5.2) (n = 4) and 10(4.2) FFU SAD P5/88 (n = 5) by the same route. On days 106 and 196 post vaccination 10 raccoon dogs and 16 foxes were challenged with a relevant street virus, respectively. All 10 raccoon dogs vaccinated with 10(6.3) (n = 5) or 10(5.7) FFU SAD P5/88 (n = 5) survived the challenge, whereas all control animals (n = 5) died of rabies. Two foxes vaccinated with 10(4.2) FFU and one fox vaccinated with 10(5.2) FFU died of rabies on day 7, 17 and 12 post infection, respectively. Also all control foxes succumbed to rabies. Our findings demonstrate that SAD P5/88 is not only an effective vaccine for oral vaccination of foxes but also for that of raccoon dogs.

Effect of the contents and form of rabies glycoprotein on the potency of rabies vaccination in cattle

One of the methods used for controlling cattle rabies in Brazil consists of vaccination. Sometimes, however, rabies occurs in cattle supposedly protected. Since rabies vaccine batches are officially controlled by tests performed on laboratory animals, it is questionable whether the minimal mandatory requirements really correspond to immunogenicity in the target species. We have analyzed the association among potencies of rabies vaccines tested by the NIH test, the contents and form (free-soluble or virus-attached) of rabies glycoprotein (G) in the vaccine batches, and the virus-neutralizing antibodies (VNA) titers elicited in cattle. No correlation was found between G contents in the vaccine batches and the NIH values, whatever the presentation of G. There was no correlation either between NIH values and VNA titers elicited in cattle. There was, however, a positive correlation (r = 0.8681; p = 0.0001) between the amounts of virion-attached G present in the vaccine batches and VNA elicited in cattle. This was not observed when the same analysis was performed with total-glycoprotein or free-soluble glycoprotein. The study demonstrated that NIH values can not predict the effect of the immunogen in cattle. On the other hand, the quantification of virus-attached rabies glycoprotein has a strong correlation with VNA elicited in cattle.

Immunogenicity, safety and lot consistency in adults of a chromatographically purified Vero-cell rabies vaccine: a randomized, double-blind trial with human diploid cell rabies vaccine

The immunogenicity and safety of a chromatographically purified rabies vaccine (CPRV) was evaluated using US veterinary medical students. In the first study, 242 healthy adults were enrolled in a randomized, modified double-blind, multicenter trial and received five doses of either CPRV or human diploid cell vaccine (HDCV) by intramuscular injection on days 0, 3, 7, 14, and 28 concurrently with human rabies immunoglobulin in a simulated post-exposure prophylaxis regimen. Post-immunization titers in the CPRV and HDCV groups reached 0.5 IU/ml (the WHO-recommended minimally acceptable titer) or greater in all subjects in both vaccine groups by day 14 and remained above that level through day 90. In the second study, 438 healthy adults were enrolled in a randomized, double-blind, multicenter trial and assigned to receive five doses from one of three lots of CPRV by intramuscular injection on days 0, 3, 7, 14, and 28 in a simulated post-exposure prophylaxis regimen to evaluate lot consistency. Post-immunization titers rapidly increased to over 0.5 IU/ml by day 14 for all subjects and remained above that level through day 42 when the study was terminated. The three lots were considered equivalent. The percentage of subjects with at least one local reaction during the five-dose regimen was slightly lower in the CPRV group than in the HDCV group (P=0.06). The most frequently reported local reaction for all doses of vaccine was pain at the injection site. Headache, myalgia, and malaise were the most frequently reported systemic events. The percentage of subjects with at least one systemic event was significantly lower for CPRV (P=0.0084). No vaccine-related serious adverse reaction was reported in these studies. The results of these studies indicate that CPRV administered intramuscularly to healthy adults is immunogenic and is associated with fewer local and systemic reactions than HDCV.

Effect of maternal immunity on the immune response to oral vaccination against rabies in young foxes

OBJECTIVE

To determine effect of maternal antibodies on immune response to oral vaccination against rabies in young foxes.

ANIMALS

250 cubs from 48 vixens.

PROCEDURE

Sera were obtained from cubs of 36 vaccinated (maternally vaccinated [MV+]) and 12 nonvaccinated (MV-) vixens between 23 and 71 days of age and tested for neutralizing antibodies. Seventy-one MV+ cubs and 33 MV-cubs were vaccinated orally with modified-live virus vaccine SAD B19. Geometric mean titer (GMT) was determined in these cubs approximately 21, 39, and 57 days after vaccination. In a subsequent experiment, 10 vaccinated MV+ cubs, 6 vaccinated MV- cubs, and 6 control cubs were challenge inoculated with virulent rabies virus approximately 100 days after vaccination.

RESULTS

Serum GMT of nonvaccinated MV cubs (0.23 U/ml) was significantly greater than that of non-vaccinated MV- cubs (0.15 U/ml). The GMT of vaccinated MV+ cubs 21, 39, and 57 days after vaccination were 2.85, 2.11, and 0.79 U/ml, respectively, and were significantly less than those of vaccinated MV- cubs (12.19, 6.76, and 4.02 U/ml, respectively). All challenge-inoculated cubs with GMT < 0.5 U/ml succumbed to rabies.

CONCLUSION AND CLINICAL RELEVANCE

Partially impaired immune response in cubs < 8 weeks old from vaccinated vixens causes insufficient protection against rabies. Inhibition of the immune response persists longer than the period during which maternal antibodies are detectable. Thus, oral vaccination campaigns for young foxes in areas where vaccination has been performed need to be reconsidered.

[Clinical endpoints during rabies vaccine control tests]

All warm-blooded animals, including humans, are susceptible to rabies. The infection with the virus leads inevitably to the death of the recipient. Vaccines and anti-serums are at present the only possibility to prevent rabies infections in the human and veterinary medicine. In order to be able to guarantee the production of a reliably safe and effective vaccine, each batch has to be tested. These tests contain animal experiments. Alone for efficacy tests of rabies vaccines done for each batch far over one hundred mice are used. In a defined time period in challenge experiments the number of deaths rates of immunised animals are compared with non vaccinated control animals. At present several replacement methods for this test are in development. However, so far none of them has been validated in an international multicenter study. The modifications necessary for example in the WHO (World Health Organization) or O.I.E. (Office International d"Epizooties) guidelines will need several more years. Therefore, this test method will be internationally used in the foreseeable future. In order to avoid unnecessary suffering of the animals, we looked for signs, which can be used to replace lethality as criterion. For this purpose score-sheets were developed, on which the observed clinical signs were recorded. The decrease of body-temperature, which was measured with transplanted transponders, occurred too late to be usable. A clear reduction of the body weight is the earliest sign of an illness. Slow and circular movements, followed by cramps and paralyses, are the first neurological symptoms of rabies. The combination of these parameters can serve as a reliable indicator for humane endpoints. This saves the mice on average between four and five days of the most stressful phase of the experiment and is a clear "refinement" of the test conditions in the sense of the 3R. A video which shows the clinical signs is available.

Stability of attenuated live virus rabies vaccine in baits targeted to wild foxes under operational conditions

The viability of an attenuated live virus rabies vaccine in a bait targeted to red foxes was examined under various operational conditions in a series of experiments in Ontario. The virus was relatively stable over a 28-day period in the field, losing a mean 0.5, s = 0.2 log10 of virus titer. The micro-environment into which the bait was placed (open cultivated field, grassy meadow, wooded grove, sun or shade) did not make an appreciable difference in the viability of the virus. There was no significant difference (P < or = 0.05) between mean ambient temperatures and the temperature of fluids in blister packs of baits placed in sun or shade. Sixty-three percent of foxes fed baits exposed to sun and shade conditions for 21 days (titer 10(6.2) tissue culture infective doses per 1 mL) developed rabies virus-neutralizing antibodies. Storage of vaccine baits at -30 degrees C prior to bait distribution was important in maintaining virus viability.

[Studies on the manufacture and immunogenicity of purified rabies vaccines on humans Vero cell]

OBJECTIVE

Using Vero cell as basic cultural material to improve the quality of rabies vaccines and to produce rabies vaccines for humans.

METHODS

CTN-1V10 strain were used for production. Vero cell of 150th generation were used for cultivation. Rotating cultivatal method with rotating bottle was used. Fluids with virus were collected at different time. Puritied rabies vaccine was produced on Vero cell after clarification, condensation, purification and extermination. A batch of vaccines made by this techniques were used for immunological observation. Sixty-three people were injected with this rabies vaccine according to the procedure of time of exposure. Thirty of them were injected with vaccines made in France (Verorab) while the others were injected with vaccines to be tested. Side effect and neutralizing antibody were recorded.

RESULTS

The quality of this newly developed rabies vaccines has met the quality set by WHO. After all dosages of injection, the rates of positive antibody were both 100% in two groups. The neutralizing antibody among testing group was 11.94 IU/ml comparing with control as 11.69 IU/ml.

CONCLUSION

Purified rabies vaccines on Vero cell for humans had reasonable manufacture technique and less little effect with good technological imnunogenicity.

Oral immunization against rabies: afterthoughts and foresight

The article contains personal views on some issues that are frequently addressed in discussions about rabies control, and on some related topics that are often overlooked. The first field applications of oral wildlife rabies immunization in the Swiss Rhone Valley were preceded by many years of international cooperative studies on efficacy and safety. They were significant "faits accomplis" that facilitated similar endeavors in other countries. Some aspects of the residual pathogenicity of oral rabies vaccines are discussed. The field efficacy of oral wildlife immunization is the outcome of complex interactions between vaccine and bait attributes, bait distribution procedures, and habitat properties. Significant difficulties hinder the interpretation of field observations on efficacy. Though oral wildlife immunization is not an animal welfare act and not a conservationist achievement, it is an attempt at zoonosis control intended to protect human health and prevent economic losses.

Evaluation of standard reagents for radial-immunodiffusion assays. In vitro control of rabies vaccines

The RID assay is one of the in vitro methods used for in-process control in the production of rabies vaccines for veterinary use. It has been shown to be very useful for determining antigen concentration in the final bulk product. The work presented in this paper, including the production and standardization of candidate standard reagents for use in the Radial Immunodiffusion Assay (RID) was carried out at the Pan American Institute for Food Protection and Zoonoses (INPPAZ/PAHO/WHO). The study was completed with the cooperation of the Faculty of Veterinary Sciences, National University of La Plata (NULP), Argentina, where the validation of the proposed standards and the quality control of samples from 28 different batches of rabies vaccines produced with Pasteur strain rabies virus (PV) in BHK cells were performed. The activity of the vaccines was determined by in vivo (NIH) and in vitro (RID)assays. The results of the candidate reagents for the reagent standardization tests showed stability, sensitivity and reproducibility. The Relative Potency the 1.2 between the problem vaccines and the reference vaccine was estimated by variance and regression analysis. The results of our validation study show that the INPPAZ (PAHO/WHO) is capable of producing and distributing the above-mentioned standard reagents, as well as of providing support for the incorporation of the RID technique (sensitive, rapid and inexpensive) to the laboratories that manufacture rabies vaccines in Latin America and the Caribbean.

Efficacy of an oral vaccinia-rabies glycoprotein recombinant vaccine in controlling epidemic raccoon rabies in New Jersey

A field trial to evaluate the efficacy of an oral vaccinia-rabies glycoprotein recombinant virus vaccine in controlling epidemic raccoon (Procyon lotor) rabies was conducted by distributing 180,816 doses (10(8.2)TCID50/ml) of vaccine in wax ampules within fish-meal polymer baits at a rate of 64 doses/km2/treatment throughout a 552 km2 area, forming an 18 km wide band across the northern Cape May Peninsula of New Jersey (USA). Vaccination treatments were conducted in the spring and fall between May 1992 and October 1994 from a helicopter along ecotones and from motor vehicles along roads. Vaccine-laden baits were removed by animals from tracking stations within 3 wk and 61% of the identifiable tracks were those of raccoons. Tetracycline incorporated in the baits as a biomarker was detected in 155 (73%) of the vaccination area raccoons following the fall 1993 and spring 1994 vaccinations. Eleven (61%) of the raccoons sampled in the same time period seroconverted (> or = 0.5 IU) in response to rabies virus glycoprotein. A raccoon diagnosed with rabies from the northern border of the vaccination area on 30 April 1993 provided the first evidence that the barrier was being challenged by the rabies epidemic. The prevalence of rabies in raccoons from the vaccination area for the first year (10%, n = 96) and second year (8%, n = 61) of challenge was reduced more than six-fold by vaccination compared to unvaccinated raccoons from northern adjacent surveillance areas during the corresponding first (65%, n = 189) and second years (53%, n = 43). Vaccination also effectively reduced by three-fold the rate at which the epidemic moved through the raccoon population (15 km/yr). The breach of the vaccination area resulted in a resumption of the high rate (43 km/yr) of epidemic movement and a significant nine-fold increase in rabies prevalence (77%, n = 47). The maximum linear movement (12.9 km) among five ear-tagged rabid raccoons in the study area was significantly greater than that of 19 normal radio-collared raccoons (2.58 km) in the area. These large movements of rabid raccoons, together with relocation of nuisance raccoons, spillover of raccoon rabies in skunks (Mephitis mephitis) and other species, insufficient funding and a decision to discontinue the program in 1994 (which could have resulted in insufficient population immunity among raccoons in the vaccination area) may have contributed to the eventual breach of the barrier.

Effectiveness of SAG1 oral vaccine for the long-term protection of red foxes (Vulpes vulpes) against rabies

Three groups of 10 foxes were vaccinated by the direct oral instillation of 2 ml of SAG1 rabies virus vaccine containing 10(6) MICLD50 (10(7) TCID50/ml) infectious viral particles/ml. SAG1 is a natural variant of the attenuated rabies vaccine strain SAD Bern and was selected in the presence of monoclonal antibodies. The strain is devoid of residual pathogenicity for the fox and the highly susceptible adult laboratory mouse by the oral, intramuscular and intracerebral routes. The foxes were challenged six, 12 and 18 months later with a virulent vulpine street rabies virus (GS 7-1-1). They all survived, whereas seven of eight unvaccinated control foxes died.

The design of veterinary vaccination programmes

The optimal design of a veterinary vaccination programme depends on both the characteristics of the vaccine and the epidemiology of the pathogen or parasite. Relevant vaccine characteristics are the proportion of those vaccinated that are initially protected, the duration of protection and the coverage achieved by the vaccination programme. The most important epidemiological parameter is the basic reproduction number, R0. Mathematical theory can integrate this information to address such questions as: whether it is possible to eliminate an infection; what proportion of hosts must be vaccinated to achieve this: what age should hosts first be vaccinated; and at what interval should hosts be revaccinated? Examples of rabies in foxes and foot-and-mouth disease in cattle suggest that theory can be used to guide the design of vaccination programmes.

Potency of veterinary rabies vaccines in The Netherlands: a case for continued vigilance

Commercial rabies vaccines, used by veterinarians in the Netherlands, were collected for testing in the mouse potency test. Of the six vaccines tested, two were clearly below the minimal requirements for potency of 1.0 IU. Of these six vaccines the rabies virus glycoprotein (GP) and nucleoprotein (NP) contents were determined in an antigen competition ELISA. The GP content proved to correlate well with the potency found in the mouse potency test (r = 0.95, p < 0.01), whereas no such correlation was found for the NP content (r approximately 0, p > 0.05). After the manufacturers were told about the results, one of the two vaccines that did not comply with the requirements was withdrawn from the market. Measurement of the GP content of a second lot of the remaining vaccines indicated that sufficiently high levels of GP were present in all five. Additional in vivo testing in mice for efficacy against intracerebral challenge with the Dutch bat rabies virus EBL1-12 resulted in acceptable levels of protection with four of these five vaccines of the second lot. The data presented illustrate the need for continued potency evaluation of veterinary rabies vaccines in the Netherlands.

[Protective effect in mice of the live rabies vaccine produced using the Göttingen bioreactor]

For the control of urban rabies in developing countries, the SAD-virusstrain was used in the Göttingen two-step Bioreactorsystem as a model-virus for oral vaccine production. The quality of the antigen had been tested by challenge. In the Bioreactorsystem, controlled by computer, a high standard of cell quality and cell density up to 6 x 10(6) cells/ml had been maintained. The high cell quality is correlated to high proliferation of rabies virus. Virus titres up to 10(8.5) pfu/ml were reached. The protectivity of the antigen had been tested by challenge. In comparison to a commercial vaccine with a PD50 of 10(-1.92) the SAD-Antigen of the Göttingen Bioreactorsystem reached a PD50 of 10(-1.63) by a challenge doses of 70-75 MLD50.

Environmental safety assessment of vaccines derived from biotechnology

Products derived from biotechnology are generally safer than previous products obtained by conventional, more empirical methods. Given the great variety of biotechnology-derived products and use situations, risk assessment procedures must be based on a case-by-case analysis. It is therefore difficult to propose a generic, well-defined risk assessment procedure. In the case of vectored vaccines, two main risks must clearly be assessed: the possible risk of tissue or species tropism modification, with special regard to non-target species, the risk of recombination with wild counterparts of the vector. This paper begins with a classification and description of the main biotechnology-derived products to be used in veterinary medicine, including deoxyribonucleic acid (DNA) vaccines, and then attempts to define general rules for the risk assessment of each category of products.

Microbial contaminants found in low egg passage rabies vaccine used in Nigeria

Bacteriological and mycological examinations (cultural and biochemical characteristics) identified 4 pathogenic organisms as contaminants in 6 out of 7 LEP batch 20 rabies vaccines produced 1990 in Nigeria. Cryptococcus neoformans and Penicillium spp. were isolated from 5 vaccine samples, while one sample additionally also contained Rhizopus and Pseudomonas. One vaccine sample was negative for microbial contaminants. Improper conditions of vaccine production and storage are discussed.

[Modifications to a method of controlling the immunogenic activity of rabies vaccines]

To determine the immunogenic potency of different rabies vaccines, they were tested in the modified test, originally developed by the National Institutes of Health (USA). In this modification the mice used in the test were challenged with strains Vnukovo-32 and Moskva instead of strain CVS, and the vaccine was introduced not in two injections, but in a single injection. The study revealed that the use of test strain Vnukovo-32, homologous to the production vaccine strain, enhanced the absolute potency of vaccines but produced no effect on the relative potency when used with the similarly prepared reference agents. A single injection of the vaccine in the test for immunogenic potency was found to produce no changes in the results of tests for relative immunogenic potency. However, this modification needs further more extensive trials and discussion.

Rabies vaccine standardization: International Collaborative Study for the Characterization of the fifth International Standard for Rabies Vaccine

A collaborative study was carried out to establish a replacement for the International Standard for Rabies Vaccine, the stocks of which are exhausted. Three rabies vaccines for human use derived from different rabies virus strains and prepared on different cell culture substrates were compared with the International Standard for Rabies Vaccine using in vivo and in vitro assay methods in a collaborative study involving 14 participants. The proposed fifth International Standard (PISRAV) which was derived from the same virus strain as the present international standard preparation, the Pitman Moore (PM) strain, was found to be approximately twice as potent relative to the International Standard in immunogenicity assays as in antigenicity assays. On the other hand another vaccine, derived from the LEP strain, was considerably more potent in antigenicity assays than in immunogenicity assays. The glycoprotein of the proposed replacement standard measured in antigenicity assays appeared to be stable at +37 degrees C for 245 days, whereas the immunogenicity of the proposed replacement vaccine was sensitive to this heat treatment and the vaccine lost 66% of its immunogenic potency. The results of this study indicate that the NIH protection test should continue to form the primary basis for potency assay of rabies vaccine as glycoprotein content does not appear to correlate with immunogenic potency for different types of vaccine. The vaccine coded PISRAV has been established as the fifth International Standard for Rabies Vaccine and a potency of 16 International Units of Rabies Vaccine (based on the immunogenicity assays) assigned to the contents of each ampoule. Each ampoule has also been assigned a unitage of 10 IU of PM Rabies Virus Glycoprotein and 135 IU of PM Rabies Virus Ribonucleoprotein.

Approaches for genetic purity testing of live recombinant viral vaccines using a human adenovirus:rabies model

A two part purity testing regimen for genetically engineered live viral vaccines is described using a human adenovirus 5: rabies glycoprotein gene recombinant as a model vaccine. Initially, restriction endonuclease analysis of the recombinant viral genome verified the integrity of the recombinant construct and identified the vector genome. The second stage employed the polymerase chain reaction to facilitate a more detailed study of the target rabies glycoprotein cassette. The size of the target region was predicted from known nucleic acid sequence information and compared to that obtained after electrophoresis with molecular weight standards. Digestion of the polymerase chain reaction product with a second restriction endonuclease cleaved the target into a number of small fragments. Resolution of the fragments by gel electrophoresis allowed analysis of the target region alone, verifying its identity and integrity.

Studies on the stability of a human adenovirus-rabies recombinant vaccine

Human adenovirus type 5 containing the rabies virus glycoprotein gene (rHAd-RG1) has potential for the oral vaccination of animals. The stability of this recombinant was tested indoors and outdoors by measuring the loss in virus infectivity. Under indoor conditions the stability of the recombinant virus was studied in an egg yolk-containing commercial stabilizer and a simple buffered salt solution (EBSS; Earle's balanced salt solution) at 4 degrees C and room temperature (24-25 degrees C). Over 16 days, there was a more rapid loss in virus titer at room temperature than at 4 degrees C in both suspending media; however, these differences were slight and may be significant when the overall stability of the vaccine is considered. When the virus was mixed with either 10% (w/v) fox or skunk feces or EBSS, placed on stainless steel disks and the disks kept under ambient conditions (air temperature 24-25 degrees C; relative humidity 45-50%), there was a more rapid decline in virus titer in the fecal suspensions (3% remained after 72 h) than in EBSS (26% remained after 72 h). When bait-coated blister packs of the vaccine were placed in an outdoor location in the fall (October) season, there was a larger drop in the virus titer for vaccines placed in the sun (54% over 32 days) than for those in the shade (40% over 32 days). Incorporating proteinaceous stabilizers in the vaccine samples for outdoor study showed virus stability was not enhanced in their presence.(ABSTRACT TRUNCATED AT 250 WORDS)

[Thermostability of rabies vaccine, type Fuenzalida & Palacios, for human use]

Ten lots of Fuenzalida & Palacios type antirabies vaccine for human use, produced at the Instituto Butantan (São Paulo, Brazil) were stored at temperatures of 45, 37, 28 and 2-8 degrees C. The potency of each lot was determined in samples taken at varied time intervals using the NIH method and lots presenting antigenic values > or = 0,3 were considered satisfactory for use. After 2 hours at 45 degrees C the antigenic value of one out of 10 lots tested was found to be less than the minimum required value. At 37 degrees C all lots maintained satisfactory antigenic values until the third day of storage, whilst at 28 and 2-8 degrees C the potency was fully maintained, respectively for 10 and 360 days. At the ideal temperature of 2-8 degrees C, 100% of the tested vaccines maintained the minimum required antigenicity for a longer period (16 months) than the expiration time of 6-12 months usually recommended for this type of biological produced in Latin American and Caribbean countries. Thus, the obtained data suggested that in countries still producing Fuenzalida & Palacios type vaccine, the expiration tim could be extended to 16 months, what could prevent the unnecessary discarding of products still in useful condition.

[Comparison of PVRV and HDCV rabies vaccines as to immunity, reliability and protective value]

World Health Organization (WHO) recommends a new Inactivated Rabies Vaccine grown on Vero Cells, (PVRV: Purified Vero Rabies Vaccine) with the vaccine cultivated on Human Diploid Cells (HDCV: Human Diploid Cell Vaccine), for both pre and post-exposure prophylaxis. Following the widespread use of HDCV and PVRV, many comparative clinical trials have been conducted, studying the safety and predictive values of these two vaccines. In the present study, using the schedule recommended by the WHO for preexposure prophylaxis, days on 0, 7 and 21, we vaccinated 90 healthy male volunteers, age ranged between 18 and 24 (mean 20) and may expose to a risk of rabies. These 90 volunteers randomly divided into 3 different groups with 30 people in each. First group vaccinated by PVRV, 2nd by HDCV and the last group by placebo (PS) double blind. The neutralizing antibody titration was measured by Rapid Immunofluorescence Focus Inhibition Test (RFFIT) on days 0, 7, 21, 28 and 60 in Laboratories of Pasteur-Merieux, Lyon-France. On day 21, in both PVRV and HDCV group the neutralizing antibody titres have occurred and the difference was not statically significant (P less than 0.05). No serious side-effects occurred with either vaccine, although some vaccinees complained of redness, induration or local pain and exceptionally of fever, and lymphadenopathy. The geometric mean of antibody titres shows a higher titre in both PVRV and HDCV group on the 60th day of following 1st vaccination. Suggesting that a year-long protection could easily be provided with the both vaccines, till to the 1st booster dose administration.