Neuraminidase content of influenza vaccines and neuraminidase antibody responses after vaccination of immunologically primed and unprimed populations.

Vaccines prepared with influenza A/swine/1976/37-like virus contained neuraminidase activity comparable to that of H3N2 vaccines, whereas little neuraminidase activity could be detected in influenza A/New Jersey/76 vaccines. In single-dose vaccine studies, A/swine/1976/37-like split-virus vaccine induced antibody to neuraminidase (NAAb) in about 20% of children younger than 18 years and this NAAb response was better than or equal to the antibody response to the vaccine's hemagglutinin (HAAb). In immunologically primed adults, the NAAb response to a single dose of Hsw1N1 or H3N2 vaccine was 38%-54%, but this value was about 1.7-fold lower than that for HAAb response. Children six to 17 years old given two doses of A/swine/1976/37-like vaccine had an overall 70% NAAb response, whereas children of similar age had an overall 30%-48% NAAb response to two doses of A/Victoria/3/75 (H3N2) virus. The findings support a hypothesis that the NAAb response to influenza vaccines can be suppressed if subjects receiving the vaccine are immunologically primed to its hemagglutinin component. NAAb responses in the absence of HAAb responses occur in only about 5% of vaccinated persons who are immunologically primed to both the hemagllutinin and neuraminidase of the vaccine.