Scholarly article on topic 'Simulated post-exposure rabies vaccination with purified chick embryo cell vaccine using a modified Thai Red Cross regimen'

Simulated post-exposure rabies vaccination with purified chick embryo cell vaccine using a modified Thai Red Cross regimen Academic research paper on "Clinical medicine"

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{Rabies / "Rabies prophylaxis" / "Rabies vaccines" / "Intradermal vaccination"}

Abstract of research paper on Clinical medicine, author of scientific article — S.N Madhusudana, T.V Sanjay, B.J Mahendra, M.S Suja

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

Academic research paper on topic "Simulated post-exposure rabies vaccination with purified chick embryo cell vaccine using a modified Thai Red Cross regimen"

International Journal of Infectious Diseases (2004) 8,175-179

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

S.N. Madhusudana3*, T.V. Sanjayb, B.J. Mahendrab, M.S. Sujaa

a Department of Neurovirology, National Institute of Mental Health & Neurosciences, PN No. 2900, Hosur Road, Bangalore 560029, India

b Department of Community Medicine, Kempegowda Institute of Medical Sciences, KR Road, Bangalore 560004, India

Received 1 April 2003; received in revised form 28 July 2003; accepted 30 July 2003 Corresponding Editor: Jane Zuckerman, London, UK

Summary Objectives: Currently, two intradermal regimens for the administration of cell culture rabies vaccines are approved by the WHO for rabies post-exposure prophylaxis: the two site Thai Red Cross regimen (TRC) and the eight site regimen. For the TRC regimen the volume of vaccine recommended per dose is 0.1 ml of purified Vero cell rabies vaccine (PVRV) and 0.2 ml of purified chick embryo cell vaccine (PCEC). The objective of the present study was to evaluate comparatively the immune response to PCEC and PVRV vaccines administered by the TRC regimen using a uniform dose of 0.1 ml of vaccine.

Methods: Forty-two subjects received TRC regimen (2-2-2-0-1-1) with 0.1ml of PCEC vaccine and 38 subjects received the same regimen with PVRV. The rabies neutralizing antibody response in these subjects on days 10, 28, 90 and 180 was determined by the standard mouse neutralization test (MNT).

Results: There was adequate antibody response with both the vaccines and 100% seroconversion was observed by day 10. Furthermore, the antibody titers obtained with PCEC did not differ significantly from those obtained with PVRV on all days tested (p > 0.05).

Conclusions: It can be concluded from the results that an adequate antibody response can be obtained with PCEC vaccine when administered by the TRC regimen even after reducing the quantity of vaccine from 0.2 ml to 0.1 ml per intradermal dose. The feasibility of using this regimen in true post-exposure cases needs to be further evaluated.

© 2004 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.

KEYWORDS

Rabies;

Rabies prophylaxis; Rabies vaccines; Intradermal vaccination

Introduction

'Corresponding author. Tel.: +91-80-699-5128/5129; fax: +91-80-656 4830.

E-mail address: mshampur@hotmail.com (S.N. Madhusudana).

Dog bites, post-exposure vaccination and human deaths due to rabies are significant health problems in developing countries, including India. The

1201-9712/$30.00 © 2004 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijid.2003.07.001

World Health Organization (WHO) estimates that around 50,000 rabies deaths are currently reported every year, with India alone accounting for 30,000 deaths.1 Nearly two million people receive post-exposure vaccination in India, which has an estimated dog population of 20 million.2

Recently, some Asian countries including Sri Lanka and Thailand have significantly reduced rabies deaths in humans mainly due to the discontinuation of the Semple vaccine and the introduction of a cost-effective intradermal (ID) vaccination with highly potent and safe cell culture vaccines. At present, three types of cell culture rabies vaccines are available in India i.e. the purified chick embryo cell vaccine (PCEC); the purified Vero cell rabies vaccine (PVRV) and the human diploid cell vaccine (HDCV). However, conventional intramuscular (IM) dosage schedules with these vaccines will not be affordable for the majority of the exposed people.

An economical ID vaccination for post-exposure prophylaxis was approved by the WHO in 19923 and subsequently endorsed in 1996.4 Two regimens were approved. i.e. the Thai Red Cross regimen (TRC) in which 1/5 of the IM dose of either PVRV or PCEC is administered ID on days 0, 3, 7, and on days 28 and 905 and an eight site regimen (applicable to only PCEC and HDCV) in which 0.1 ml of vaccine is administered at eight sites on day 0, at four sites on day 7 and at one site on days 28 and 90.6 As per these recommendations, in the TRC regimen, one has to administer either 0.1 ml PVRV or 0.2 ml of PCEC per dose. Subsequent to these recommendations, some studies in Thailand demonstrated the immunogenicity, safety and efficacy of the PCEC vaccine when administered in a 0.1 ml (1/10 of IM dose) dose using the TRC regimen.7-9 If the PCEC vaccine is administered under this regimen, it will become more economical than PVRV, as the total quantity of vaccine in a single vial after reconstitution is 1 ml and hence twice the number of patients can be vaccinated in comparison to PVRV.

The WHO expert committee meeting held in June 2000 recommended this regimen for national authorities to consider but also cautioned that more data need to be generated.10 The immunogenicity of such a regimen using a reduced quantity of the PCEC vaccine in the Indian population has not been reported so far. India is currently on the threshold of introducing ID regimens in major anti-rabies treatment centres across the country and data from such studies will become important.

Keeping this in view we administered the PCEC vaccine under this regimen to 42 healthy people who needed pre-exposure prophylaxis and evaluated the immune response in comparison to the

response observed in 38 people who were administered PVRV under the same TRC regimen.

Materials and methods Subjects

Forty-two people working in the Infectious Diseases Hospital in Bangalore, and 38 people working in the neurological intensive care units of the National Institute of Mental Health & Neurosciences (NIMHANS) in Bangalore who were likely to treat patients with rabies were included, as they needed pre-exposure rabies prophylaxis. Of these, 42 people (21 adult males and 21 adult females, age range 21-49 years, mean age 32 years) were immunized with the PCEC vaccine and 38 (20 adult males and 18 adult females, age range 25-52 years, mean age 30 years) were immunized with the PVRV vaccine. All the subjects in the PCEC group were from the Infectious Diseases Hospital, while subjects in the PVRV group belonged to NIMHANS. All were recruited during the same period and all were physically healthy and were not taking any medication.

Vaccines and regimen

The PCEC vaccine (Rabipur®, Chiron Vaccines, batch No. 653, potency >2.5 IU) and the PVRV vaccine (Verorab, Aventis Pasteur, batch No. U 1240, potency >2.5 IU) were used in this study. The vaccines were reconstituted with 1 ml of sterile water for injection in the case of PCEC and 0.5 ml in the case of PVRV and inoculated in a 0.1 ml dose ID on two sites (over upper arm) on day 0, 3 and 7 and at one site on day 28 and 90. As subjects were vaccinated in groups, the diluted vaccine was used at one time and there was no wastage of vaccine. Each subject was inoculated with a separate 1 ml disposable insulin syringe. The subjects were interrogated and physically examined on each occasion for evidence of any side-effects. Blood samples were collected on day 0 (prior to immunization) and on days 10, 28, 90 and 180 after immunization.

Estimation of antibody titers

The rabies neutralizing antibody titers in the serum samples were estimated by the mouse neutralization test (MNT) as advocated by the WHO.11 The challenge virus standard (CVS 11) used in the test was obtained from the Central Research Institute, Kasauli. The antibody titers of serum samples were expressed in International Units (IU/ml) as

compared to an in-house reference serum previously calibrated against second international standard of anti-rabies immunoglobulin serum with a known potency of 30IU (obtained from National Institute for Biological Standards and Control, NIBSC, UK). The in-house reference serum was prepared from immunized rabbits and was calibrated by the MNT in parallel with the international standard. The antibody titer of the in-house reference serum was determined after running duplicate tests. This in-house reference serum has 15IU/ml of potency in comparison to the international standard. For conducting MNT, prior permission from the institutional animal ethics committee was obtained and the experimental mice were caged and looked after as per the guidelines in force.

Statistical analysis

The neutralizing antibody titers observed in the two groups were expressed as arithmetic means with standard deviations. The difference in the antibody titers observed in the two groups was analyzed by using a Student's t-test.

Results

None of the serum samples had detectable antibody titer on day 0 prior to vaccination. There were two dropouts after the 2nd dose of the vaccination in the PCEC group because these subjects were unexpectedly deputed to another hospital.

Blood samples were obtained from 40 people on day 10, 38 people on days 28 and 90 and 35 people on day 180 in the PCEC group. In the PVRV group blood samples were obtained from 38 people on day 10, 35 people on days 28 and 90 and 33 people on day 180. The antibody titers observed with the two vaccines are reported in Table 1. It is evident that there was 100% seroconversion in both the groups

Table 2 Side-effects observed with the PCEC vaccine and the PVRV administered by the TRC regimen.

Side-effectsa Type of vaccine

PCEC PVRV

Pain Itching Erythema Induration Fever Arthralgia 4/42 (9.5%) 3/42 (7.1%) 2/42 (4.8%) 2/42 (4.8%) 1/42 (2.4%) 1/42 (2.4%) 2/24 (8.3%) 2/24 (8.3%) 1/24 (4.2%) 1/24 (4.2%) 0/24 0/24

PCEC: Purified chick embryo cell vaccine fied vero cell rabies vaccine. a Side-effects observed on days 3 and 7. . PVRV: Puri-

by day 10. Moreover, the antibody titers with the two vaccines on all days tested did not differ significantly (p>0.05) with titers considerably above the minimum required titer of 0.5 IU/ml of serum on all days tested. There were minor side-effects such as local erythema, itching and induration observed with both the vaccines on day 3 and 7 (Table 2). However these were self-limiting and required no treatment.

Discussion

The current rabies vaccines prevent rabies in exposed persons by the induction of neutralizing antibodies.12 The amount and speed of antibody induction is crucial for disease prevention. The WHO has recommended a minimum antibody titer of 0.5 IU/ml of serum for protection against this disease.3 Studies conducted so far have clearly indicated that all the ID regimens recommended can induce antibody titers considerably above the minimum required for protection. The initial doubt as to whether a reduced volume (0.1 ml instead

Table 1 Mean neutralizing antibody titers (IU/ml) to the rabies virus in subjects vaccinated with the PCEC vaccine and the PVRV vaccine using the TRC (2-2-2-0-1-1) regimen.

Vaccine and subjects Neutralizing antibody titers (IU/ml)a on days

10 28 90 180

PCEC Subjects (n = 42) PVRV Subjects (n = 38) 5.8 (± 3.1) 5.9 (± 3.2) 10.9 (± 4.1) 12.1 (± 4.5) 13.1 (± 3.9) 14.3 (± 2.7) 5.7 (± 3.1) 5.9 (± 2.5)

aMean titers (± standard deviation). PCEC: vaccine. TRC: Thai Red Cross regimen. Purified chick embryo cell vaccine. PVRV: Purified Vero cell rabies

of 0.2ml) of PCEC vaccine can induce protective antibody levels if given by the TRC regimen is now resolved as evidenced by the results of studies conducted in Thailand7-9 and the present study reported here on Indian subjects. As the results of the present study indicate, 100% seroconversion was evident on day 10 and protective titers were present even six months later. The titers obtained with PCEC vaccine did not differ significantly from those obtained with PVRV vaccine (p>0.05). The side-effects observed were negligible and did not require any treatment (Table 2).

Administration of 0.2 ml of the PCEC vaccine by the ID route as recommended previously may pose practical difficulties as it tends to be more painful and the bleb formed is much larger. The alternative recommendation was to give two ID inoculations of 0.1 ml in nearby sites. However, inoculating 0.1 ml ID at two nearby sites means more injection pricks to the patient, causing more pain and inconvenience. These practical difficulties may be overcome if this newly-approved regimen is practiced.

The currently available cell culture vaccines are not economical if regular IM regimens are used. For instance, the total cost per patient of the vaccine alone is around Rs. 1,500 (US$ 30) with the use of PVRV and PCEC, which may be unaffordable by the majority of exposed people. If these vaccines are used ID the cost per patient will reduce to Rs 400 (US$ 8). Although the Semple vaccine is cheaper, the actual expenditure per patient may work out to be more than the cost of administration of cell culture vaccines by the intradermal route, if the indirect cost in terms of the number of man days lost, serious side-effects and cost of their management are also added. In a recent estimate, the cost of the Semple vaccine being administered in government hospitals and dispensaries worked out to be about Rs 200 (US$ 4.5) per patient, which is half the cost of PVRV if administered by the TRC regimen. On the other hand, if the volume per dose of the PCEC vaccine is reduced from 0.2 ml (as recommended previously) to 0.1 ml as recommended now, the cost per patient will work out at even less than the cost of the Semple vaccine. Therefore a highly potent and safe vaccine can be administered instead of the outdated and unsafe Semple vaccine, whose production was recommended to be discontinued more than a decade ago by the WHO. Therefore there is an urgent need to phase out the Sem-ple vaccine and introduce these cost-effective ID regimens.

One of the major drawbacks of abbreviated ID regimens is the possible wastage of reconstituted vaccine if it cannot be distributed amongst pa-

tients within six hours. However, a recent study in Thailand has demonstrated that the reconstituted vaccine can be stored for up to seven days at 4 °C in a refrigerator without loss of potency or fear of contamination.13 However, wastage of reconstituted vaccine may not be encountered in major anti-rabies clinics and dispensaries where a large number of patients attend on any single day.

Conclusion

To conclude, this simulated post-exposure study with the PCEC vaccine administered by the WHO-recommended TRC regimen using 0.1 ml per ID dose proved to be as immunogenic and as safe as the TRC regimen with PVRV in Indian subjects. It is now planned to extend this study to people exposed to rabies by animal bites so that data on the efficacy of this regimen can be generated.

Acknowledgements

The authors thank Aventis Pharma, Mumbai, India for the free supply of the PCEC vaccine (Rabipur®) used in this study. We also acknowledge Dr Gupta, Medical Superintendent, Epidemic Disease Hospital, Bangalore for the permission given to this study. We also thank Dr Sureshchandra, Senior Veterinary Officer, NIMHANS for supplying experimental mice for conducting MNT.

Conflict of Interest: No conflicting interest declared.

References

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