Stability of an antifertility vaccine consisting of gonadotropin subunits linked to tetanus toxoid

Abstract

The shelf life and thermal stability of an antifertility vaccine, in which gonadotropin subunits are linked to carriers such as tetanus toxoid and cholera toxin chain B and has successfully completed phase-I clinical trials at five centres in India, was studied. The vaccine adsorbed on alum was stored at three temperatures, 4°C, room temperature (20-30°C) and at 40°C, for a period of up to 1 year. The human chorionic gonadotropin (hCG) binding capacity of antibodies (peak titres) induced in rodents by the vaccine after 6 months of storage at 40°C and at room temperature were 1430±201 (mean±s.e.m.) and 1291±152 ng ml⁻¹ respectively as compared to 1075±185 ng ml⁻¹ for the vaccine stored at 4°C. The difference was not statistically significant. After 12 months of storage, the immunogenic properties of the vaccine were nearly the same irrespective of the temperature at which the vaccine was kept. The findings show that the vaccine adsorbed on alum can withstand storage up to at least one year at room temperature and at 40°C. These observations have implications for the current thoughts on storage of tetanus toxoid and diphtheria toxoid at 4-8°C, the two vaccines widely used in immunoprophylaxis, and suggest that similar investigations on these vaccines as cold chain facilities are not universally available in developing countries.