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In the fall of 1983, 53 households were enrolled in a double-blind trial of alpha 2-interferon as an intranasal spray to prevent common colds. During the winter/spring of 1984, 26 households were infected with influenza type B, as shown by isolation of the virus (19 households) and/or significant antibody titer rises (seven households). Interferon did not prevent influenza B infection or modify resulting illness. Of 37 persons shedding virus, 12 were asymptomatic. All were older than age 12 years, and 10 did not respond with antibody by any of the five test methods employed (complement fixation, hemagglutination inhibition, enzyme-linked immunosorbent assay (ELISA), neutralization, and Western blot). In contrast, of 13 symptomatic persons shedding virus from whom sera were available, 11 had significant antibody titer rises. Infection rates were highest among teenagers, but also surprisingly high among the 11 persons observed who were aged 50 years or older, four of whom were infected. The case-to-case interval in household transmission varied between one and nine days. Longer intervals of one, two, and four months between infections among family members were also observed, suggesting repeated introductions. Neither virus isolation alone nor serologic tests was sufficient to estimate infection rates.

Efficacy of intranasal recombinant alpha interferon (IFN-alpha 2b) was evaluated over a four-week period. The first 400 participants received either 1,500,000 IU of IFN-alpha 2b or placebo twice daily. Rhinovirus infections were prevented (protective efficacy, 76%). Parainfluenza infections were not prevented, but symptoms in associated episodes of disease were significantly reduced. The medication was generally well tolerated, but side effects were often observed. The most commonly reported symptom was blood-tinged mucus. A pilot study of IFN-alpha 2b or placebo administered on a once-daily dose schedule was also carried out in 150 participants. There was a suggestion of continued efficacy with reduced side effects. Overall, these findings would limit the use of IFN-alpha 2b on the twice-daily schedule to shorter time periods or to special situations in which the efficacy clearly outweighs side effects, and they encourage further examination of other dosage schedules.