HEALTH OUTCOMES AND COSTS OF COMMUNITY MITIGATION STRATEGIES FOR PANDEMIC INFLUENZA IN THE U.S

Purpose: The optimal community-level approach to control pandemic influenza is unknown.

Method: We estimated the health outcomes and costs of combinations of 4 social distancing strategies (adult social distancing, child social distancing, school closure and household quarantine) and 2 antiviral medication strategies (treatment alone or treatment and prophylaxis) to mitigate an influenza pandemic for a demographically “typical” U.S. community.  We used a social network, agent-based model to estimate strategy effectiveness.  We used data from the literature to estimate clinical outcomes and health care utilization.  Outcomes included cases averted, total quality-adjusted life years, total costs, cost per case averted and the incremental cost-effectiveness ratios (cost per quality-adjusted life-year saved) of alternative strategies.  We tested sensitivity of the results to virus infectivity (Ro, the reproductive number), case fatality rate, population compliance, and costs.

Result: The most effective strategies are multilayered interventions.  At 1% influenza mortality, moderate infectivity (R_o 2.1 or greater), and 90% population compliance, the preferred strategy is adult and child social distancing, school closure, and antiviral treatment and prophylaxis.  This strategy reduces cases in the population from 35% to 4%, averts 3,100 cases per 10,000 population, costs $2,700 per case averted and $22,000 per quality-adjusted life-year gained compared to the same strategy without school closure.  If antivirals are either ineffective or unavailable, then a strategy of adult and child social distancing and school closure reduces cases to 8% of the population, averts 2,700 cases per 10,000 population, costs $4,200 per case averted and $17,300 per quality-adjusted life-year gained compared to the same strategy without school closure.  The preferred strategies are robust to varied assumptions.  The addition of school closure to adult and child social distancing and antiviral treatment and prophylaxis, if available, is not cost-effective for viral strains with low infectivity (R_o 1.6 and below) and low case fatality rates (1% and below).  High population compliance lowers costs to society substantially when the pandemic strain is severe (R_o 2.1 or greater).

Conclusion: Multilayered mitigation strategies that include adult and child social distancing, use of antivirals and school closure are effective and, for a severe pandemic, cost effective.  Choice of mitigation strategy should be driven by the severity of the pandemic, as defined by the case fatality rate and infectivity.