title: An attenuated influenza virus vaccine: protection against homologous and heterologous strains of virus.
abstract: An effective influenza vaccine should be capable of providing protection against both the homologous virus strain and heterologous strains representing antigenic "drift". Two attenuated vaccines were evaluated, an A/Hong Kong/8/68 (H3N2) and an A/England/42/72 (H3N2) strain. Volunteers were immunized intranasally with either placebo or vaccine in a "double-blind" fashion in two doses, 2 weeks apart. Eighty-four subjects were challenged 30-100 days after the second dose with either the homologous or a heterologous strain. The heterologous strain for the A/Hong Kong/8/68 (H3N2) vaccinees was the A/England/42/72 (H3N2) virulent strain. The heterologous strain for the A/England/42/72 (H3N2) vaccinees was a virulent A/Dunedin/73 (H3N2) strain. Both vaccines led to good protection against both homologous and heterologous challenges. The protection rate against illness for the A/Hong Kong/8/68 (H3N2) vaccinees was 73% and 100% following homologous and heterologous challenges, respectively. The protection rate for the A/England/42/72 H3N2) vaccinees was 100% following both homologous and heterologous challenges. The protection rates against infection (as judged by antibody responses, irrespective of signs and symptoms) were also good. For the A/Hong Kong/8/68 (H3N2) vaccinees the rates were 73% (homologous) and 86% (heterologous). For the A/England/42/72 vaccinees, the rates were 72% and 60% respectively. Thus, immunity induced by these attenuated influenza vaccines extends to provide protection against related but non-identical influenza viruses.
mesh_terms: D000328:Adult; D000914:Antibodies, Viral; D002986:Clinical Trials as Topic; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D009980:Influenza A virus / Q000276:immunology*; D007252:Influenza Vaccines / Q000009:adverse effects; D008297:Male; D009297:Nasal Mucosa / Q000378:metabolism; D007507:Therapeutic Irrigation; D014611:Vaccination; D014613:Vaccines, Attenuated
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines; D014613:Vaccines, Attenuated