Quality Assessment of Veterinary Rabies Vaccines’ Potency Used in Thailand

Abstract

Some veterinary rabies vaccines used in Thailand had been found substandard potency. The objective of this study was to assess the potency of veterinary rabies vaccines used in country during 2017- 2019 by the standard method National Institutes of Health (NIH) test which is the in-vivo assay, and also to determine the antigen content by in-vitro assay. The potency of samples, which were collected from voluntary companies, had never been determined by the local national control laboratory. NIH assay, mice were immunized with rabies vaccine and subsequently challenged with rabies virus into the brain. The results were calculated and compared with international reference vaccine. Glycoprotein content was determined by Sandwich ELISA. The results showed that the potency from NIH assay of 11 vaccine lots from 6 registration dossiers had a range of 1.09-17.12 IU/dose. All sample lots met the minimum acceptance criteria recommended by the World Health Organization, Office International des Epizooties and European pharmacopeia which must be not less than 1.0 IU/dose. There were 2 lots which had invalid results. The glycoprotein content was determined in 29 vaccine lots from 12 registration dossiers, the results revealed that glycoprotein content had a range of 1.14-10.33 IU/dose for which there was no international specification. The result of both NIH and glycoprotein assays showed the same trend; and the vaccines from the same dossiers had similar potency values whereas the difference dossiers had different but similar values. In summary, all rabies vaccine lots met the minimum acceptance criteria. However, the potency assay should be performed on vaccines which have never been tested and should continue to monitor the potency of vaccines which are close to the minimum acceptance criteria. In addition, the determination of glycoprotein content of each vaccine should be continued to obtain enough results for criterion establishment of vaccine quality monitoring.