A Study of Influenza Virus Vaccines by a Serum-Virus Neutralization Test and by Active Immunization

Abstract

It required approximately 63 to 125 times more influenza virus vaccine to immunize mice actively against infection caused by intranasal instillation of influenza viruses, PR 8 and Weiss (type A), than it did to stimulate circulating antibodies which neutralized the same quantity of virus, the tests being carried out in identical mice and at the same time. For the Lee strain (type B), five times more vaccine was necessary to produce active immunity comparable to the protection afforded to mice against influenza virus neutralized by immune serum elicited by a small amount of vaccine. The dilution of vaccine which actively immunized mice against influenza virus stimulated the production of immune serum of higher titer than did the dilutions of vaccine which did not actively protect the mice. A measurement of the smallest amount of vaccine which would produce immune serum in mice capable of protecting other mice against approximately 10³LD₅₀ doses of virus was utilized to determine the potency of influenza virus vaccines.