Effective protection against influenza after vaccination with subunit vaccine

Immunization with an influenza subunit vaccine given in one dose about 1 month to 2 months before onset of an epidemic of influenza afforded from 80% to 90% protection in a double-blind clinical trial which was supported by isolation of virus and serological studies. In the vaccinated group, 20% failed to develop antibodies to the vaccine. Either serology tests or attempted isolation of virus alone would have failed to detect some of the cases.