For the first wave of pandemic influenza or a bioterrorist influenza attack, antiviral agents would be one of the few options to contain the epidemic in the United States until adequate supplies of vaccine were available. The authors use stochastic epidemic simulations to investigate the effectiveness of targeted antiviral prophylaxis to contain influenza. In this strategy, close contacts of suspected index influenza cases take antiviral agents prophylactically. The authors compare targeted antiviral prophylaxis with vaccination strategies. They model an influenza pandemic or bioterrorist attack for an agent similar to influenza A virus (H2N2) that caused the Asian influenza pandemic of 1957-1958. In the absence of intervention, the model predicts an influenza illness attack rate of 33% of the population (95% confidence interval (CI): 30, 37) and an influenza death rate of 0.58 deaths/1,000 persons (95% Cl: 0.4, 0.8). With the use of targeted antiviral prophylaxis, if 80% of the exposed persons maintained prophylaxis for up to 8 weeks, the epidemic would be contained, and the model predicts a reduction to an illness attack rate of 2% (95% Cl: 0.2, 16) and a death rate of 0.04 deaths/1,000 persons (95% CI: 0.0003, 0.25). Such antiviral prophylaxis is nearly as effective as vaccinating 80% of the population. Vaccinating 80% of the children aged less than 19 years is almost as effective as vaccinating 80% of the population. Targeted antiviral prophylaxis has potential as an effective measure for containing influenza until adequate quantities of vaccine are available. antiviral agents; bioterrorism; computer simulation; disease outbreaks; influenza; influenza A virus; influenza vaccine; Monte Carlo method Abbreviations: AVE, antiviral efficacy; AVE D , antiviral efficacy for symptomatic disease given infection; AVE I , antiviral efficacy for infectiousness; AVE S , antiviral efficacy for susceptibility to infection; AVE SD , antiviral efficacy for symptomatic disease; CI, confidence interval; R, reproductive number; R 0 , basic reproductive number; VE I , vaccine efficacy for infectiousness; VE S , vaccine efficacy for susceptibility; VE III , overall effectiveness.
Influenza is an annual major public health threat. In the United States, influenza epidemics usually occur during the winter months between November and April and are responsible for an average of 36,000 excess deaths per year (1). These annual epidemics are generally due to genetically drifting strains of influenza that differ slightly from previous strains (2). Each year, influenza vaccine is targeted against the strains (usually from the past year) that are expected to circulate in the next season. However, when a major antigenic shift occurs, time is insufficient to manufacture