The effect of formaldehyde on the toxicity and potency of pertussis vaccine.

Storage of concentrated suspensions of Bordetella pertussis organisms at 5 C for long periods of time in the presence of 0.02% thimerosal as well as heating at 56 C for 30 minutes cannot be relied upon to detoxify the vaccines. Our data show that the toxic thimerosal-killed vaccines can be rapidly detoxified by adding formalin to a final concentration of 0.025-0.05% and incubating at temperatures of 5-20 C for from one to three months. These formalin-detoxified vaccines are protective and meet present potency requirements for pertussis vaccine. Addition of larger amounts of formalin at higher temperatures may detoxify the vaccine but may also reduce the protective effect.