Clinical trial with "R-75" strain live, attenuated, serum inhibitor-resistant intranasal influenza B vaccine.

The "R-75" strain live, attenuated, serum inhibitor-resistant influenza B vaccine was administered intranasally by drops in two doses 14 days apart to 21 volunteers. Each vaccinee was paired with a close associate (roommate or workmate) who similarly received two doses of a placebo solution. Although about 50% of both vaccine and placebo recipients complained of symptoms after dosage, the severity of symptoms was greater in vaccine recipients. Fourfold serum hemagglutination-inhibiting antibody titer rises occurred in 38% of vaccine recipients, and four vaccines had fourfold titer rises of nasal hemagglutination-inhibiting antibody. Vaccine virus was isolated from three asymptomatic vaccine recipients. There was no virological or serological evidence of the vaccine virus spreading to placebo recipients.