International regulatory requirements for vaccine safety and potency testing: a WHO perspective&

Removal of the innocuity test from The International Pharmacopoeia and WHO recommendations for vaccines and biological products

The innocuity test was indicated as a quality control test to release pharmaceutical and biological products to the market. The test was intended to detect possible extraneous toxic contaminants derived from the manufacturing processes of the product. The test was included in WHO Recommendations and Guidelines for vaccines, biotherapeutics and blood products and in some monographs on antibiotics in The International Pharmacopoeia. Over the past years, the requirements in WHO Recommendations/Guidelines for conducting the test evolved such that it could be waived for routine release of product once consistency of production was established to the satisfaction of the NRA, or that the need for this test should be discussed and agreed with the NRA. However, some users of WHO written standards for biologicals (i.e., Recommendations, Guidelines) and WHO specifications for pharmaceuticals (i.e., The International Pharmacopoeia) requested that the innocuity test be deleted from WHO written standards based on its lack of specificity and scientific relevance. In response to that request, we studied the history of this test and its use by the member states of WHO, and the recommendations in WHO written standards. The outcomes of the study were reviewed by the relevant WHO Expert Committee on Biological Standardization and Expert Committee on Specifications for Pharmaceutical Products who then decided to discontinue this test in WHO Recommendations for vaccines and biologicals and to omit the test from The International Pharmacopoeia.

Principles of vaccine potency assays

Compared with biologics, vaccine potency assays represent a special challenge due to their unique compositions, multivalency, long life cycles and global distribution. Historically, vaccines were released using in vivo potency assays requiring immunization of dozens of animals. Modern vaccines use a variety of newer analytical tools including biochemical, cell-based and immunochemical methods to measure potency. The choice of analytics largely depends on the mechanism of action and ability to ensure lot-to-lot consistency. Live vaccines often require cell-based assays to ensure infectivity, whereas recombinant vaccine potency can be reliably monitored with immunoassays. Several case studies are presented to demonstrate the relationship between mechanism of action and potency assay. A high-level decision tree is presented to assist with assay selection.

A collaborative study of an alternative in vitro potency assay for the Japanese encephalitis vaccine

The use of inactivated Japanese encephalitis (JE) vaccines has been ongoing in East Asia for 40 years. A mouse immunogenicity assay followed by a Plaque Reduction Neutralization (PRN) Test (PRNTest) is currently recommended for each lot release of the vaccine by many national authorities. We developed an alternative in vitro ELISA to determine the E antigen content of the Japanese encephalitis virus to observe the 3Rs strategy. A collaborative study for replacing the in vivo potency assay for the Japanese encephalitis vaccine with the in vitro ELISA assay was confirmed comparability between these two methods. The study demonstrated that an in vitro assay could perform faster and was more convenient than the established in vivo PRNTest. Moreover, this assay had better precision and reproducibility compared with the conventional in vivo assay. Additionally, the content of antigen determined using the in vitro ELISA correlated well with the potency of the in vivo assay. Furthermore, this method allowed discrimination between individual lots. Thus, we propose a progressive switch from the in vivo assay to the in vitro ELISA for JE vaccine quality control.

Non-animal replacement methods for human vaccine potency testing: state of the science and future directions

NICEATM and ICCVAM convened an international workshop to review the state of the science of human and veterinary vaccine potency and safety testing methods, and to identify opportunities to advance new and improved methods that can further reduce, refine, and replace animal use. This report addresses methods and strategies identified by workshop participants for replacement of animals used for potency testing of human vaccines. Vaccines considered to have the highest priority for future efforts were (1) vaccines for which antigen quantification methods are already developed but not validated, (2) vaccines/components that require the largest number of animals, (3) vaccines that require an in vivo challenge test, and (4) vaccines with in vivo tests that are highly variable and cause a significant number of invalid tests. Vaccine potency tests identified as the highest priorities for replacement were those for diphtheria and tetanus, pertussis (whole cell and acellular), rabies, anthrax, polio vaccine (inactivated) and complex combination vaccines based on DT or DTwP/aP. Research into understanding the precise mechanism of protection afforded by vaccines and the identification of clinically relevant immunological markers are needed to facilitate the successful implementation of in vitro testing alternatives. This report also identifies several priority human vaccines and associated research objectives that are necessary to successfully implement in vitro vaccine potency testing alternatives.