Infection-permissive immunization with influenza virus neuraminidase prevents weight loss in infected mice.

In studies of infection of young Balb/c mice with a mouse virulent strain of X-31 (H3N2) influenza A virus we have shown a profound virus dose-related effect of infection on body weight. Most of this effect is prevented by prior administration of either inactivated whole virus vaccine, which prevents infection, or purified influenza virus neuraminidase, which is infection-permissive, but reduces pulmonary virus replication by 1.5 to 3 orders of magnitude. These studies support the concept of infection-permissive immunization and suggest that levels of virus replication previously shown to be antigenic can be sustained without significant systemic effects.