A multi-dose serological assay suitable to quantify the potency of inactivated rabies vaccines for veterinary use

Inactivated rabies vaccines: Standardization of an in vitro assay for residual viable virus detection

Human rabies, a neglected viral zoonosis, is preventable through domestic animals vaccination and post-exposure prophylaxis using inactivated rabies vaccines. During vaccine production, several mandatory in vivo quality control trials, such as potency, live virus, and safety, are responsible for the use of large numbers of laboratory animals. Over the years, global organizations encouraged the development of alternative methods to reduce, replace and refine the use of animals in the pharmaceutical industry. In this study we standardized an in vitro assay for determination of residual live virus combining viral isolation techniques with direct immunofluorescence detection and viral quantification by a molecular method. Standardization of viral recovery steps and quantification by RT-qPCR were performed and the combined method was shown to be 3 fold more sensitive than the in vivo assay. It was possible to identify viral suspensions cultures, which still had residual viable rabies virus particles, evidencing the importance to implement this method in quality control schemes of rabies vaccine production. In addition, this developed assay is more practical, inexpensive and less time consuming, producing results in just 4 days, which may allow greater agility in the internal quality control of the vaccine. The in vitro method may reduce 2/3^rd of laboratory animals numbers used for this purpose, since it can be applied in the intermediate quality control of inactivated rabies vaccine production.

Rabies is a viral disease that causes thousands of deaths worldwide every year, but can be preventable through vaccination of animals and humans. In the production of inactivated rabies vaccines, quality control assays use large amounts of laboratory animals. In order to reduce the number of animals in this practice, in vitro methods for residual live virus detection need to be developed. This study shows that combining two simple and effective techniques may be a safer and more accurate method for the detection of residual rabies virus than in vivo assays to evaluate inactivated vaccines and can be used as an intermediate quality control assay of vaccine production.

Possibility of Immediate Introduction of a Single-Dose Antibody Induction Test as a Refinement of the NIH Test for Inactivated Rabies Vaccine Potency Determination

Antibody induction test (AIT) is a promising candidate as a refinement of the troublesome National institutes of Health (NIH) test in the sense of animal welfare 3R approach for determination of potency of inactivated rabies vaccines for veterinary and human use. In this study, we initially try to develop AIT as a suitable alternative to NIH test, to achieve a reduction of test duration and diminish animal suffering by omitting intracerebral CVS infection and measuring humoral immunity upon vaccination. Designs of both multi-dose and single-dose AIT were examined. Biological reference preparation, batch 5 with assigned titer of 10 IU/vial, was taken as both standard and test vaccine. Six consecutive AITs were performed and eight pools of sera in each AIT were tested in triplicate by rapid fluorescent focus inhibition test. We estimated the upper detection limit and calculated test variability for individual dilutions. For multi-dose AIT, we estimated the dose-response function and performed calculations of final test results and statistical validity parameters for both linear and sigmoidal model using CombiStats program. Sigmoidal 4-parameter dose-response model was found optimal. Presented design of multi-dose AIT showed a satisfactory detection limit for testing of inactivated rabies vaccines for both veterinary and human use. However, due to nonconformity of obtained results with statistical validity criteria, we concluded that the presented model of multi-dose AIT was unsuitable for introduction in routine practice. However, we concluded that there was a realistic option for introduction of two versions of single-dose AIT. The first version would be with two standard vaccine controls and could be introduced immediately, while the second version would include testing of the sample only and rely on comparison of the induced rabies antibody level with absolute cut-off limits set in advance.

Serological profiling of rabies antibodies by enzyme-linked immunosorbent assay and its comparative analysis with rapid fluorescent focus inhibition test in mouse model

Aim:

In this study, we have used enzyme-linked immunosorbent assay (ELISA) as an alternative test to replace the cumbersome rapid fluorescent focus inhibition test (RFFIT) to ascertain the immune status of immunized mice against rabies virus.

Materials and Methods:

Rabies is a devastating disease worldwide caused by rabies virus. Proper usage of pre- or post-exposure rabies vaccine can prevent the disease transmission. In this study, mice were immunized with Vero cell-adapted inactivated rabies vaccine. RFFIT was used as a test to determine the serum neutralizing titers in infected/vaccinated mice. Seroprofiling of mice sera was done in vitro by ELISA.

Results:

Twenty-one days post-immunization, both ELISA and RFFIT assays indicated similar antibody levels in mice sera that were immunized with Vero cell-adapted inactivated rabies vaccine. Both the tests were correlated, and the linearity was verified by the regression line (R²=0.979).

Conclusion:

In this study, we profiled the serological status of Vero cell-adapted inactivated rabies vaccine through ELISA in mice model that correlated well with the OIE gold standard test RFFIT.

Development and pre-validation of a quantitative multi-dose serological assay for potency testing of inactivated rabies vaccines for human use

It is mandatory to ensure the quality of biological products used in the prevention of rabies, a zoonosis with nearly 100% lethality. Fifteen million people receive post-exposure prophylaxis yearly. The vaccine batches are assessed by the National Institutes of Health (NIH) test which has several disadvantages such as significant variability and animal welfare issues. The estimation of immunogenicity based on titration of neutralizing antibodies (NA) is not applied to the human vaccine yet. Despite this, a satisfactory concentration of NA (0.5 IU/ml) can be used as a predictor of the clinical efficacy and for estimating rabies vaccine potency. The objective of this study was to develop and pre-validate a Serological Potency Test (SPT) using the modified Rapid Fluorescent Focus Inhibition Test (mRFFIT) to determine the potency of rabies vaccines for human use, demonstrating its relevance and reliability. The results show good agreement between the potencies determined by the SPT and the NIH test. The assay was able to distinguish between potent and sub-potent lots of vaccines. The results demonstrated that SPT is a viable candidate for validation and inclusion in pharmacopeias as a reduction and refinement for the NIH test.