Advances in influenza virus vaccine research.

Influenza epidemics occur annually in the United States and are characterized by high frequencies of illness among children and young adults, high hospitalization rates among infants and older persons, and high death rates among the elderly. Vaccines that can prevent infection must stimulate anti-hemagglutinin antibody in serum and secretions; those that stimulate anti-neuraminidase antibody or T cell cytotoxic responses can reduce the severity of infection and illness or hasten recovery. Advances in vaccine research are permitting evaluation of pure subunit vaccines, new adjuvants, topical immunization, and the use of immunomodulators for enhancing immune responses. In young adults, doses of HA of up to 405 micrograms were well tolerated and provided enhanced antibody responses. Although use of a muramyl-dipeptide derivative as an adjuvant resulted in unacceptable reactogenicity, other adjuvants may be acceptable. Development of topical immunization and immunomodulators are under way. The cold-adapted live attenuated influenza virus vaccines for nasal administration are nearing availability. They are safe, immunogenic, and protective with greatest effectiveness among young children, in whom inactivated vaccines are less useful. Use among children should moderate the high frequencies of illness and hospitalization in this group and reduce spread of influenza in the community. CRV also provide an alternative to inactivated vaccines among young adults, in whom they can be equally protective.