Seasonal Influenza Case Study

Seasonal influenza is a common viral respiratory infection which typically causes mild to moderate illness in most people. Pandemic influenza occurs when a new or novel strain of influenza virus capable of spreading easily from person to person emerges. Since it is a new strain, there is often little or no immunity to it and it may spread rapidly, creating a global outbreak. An important difference from seasonal influenza is that healthy people in all age groups may be at higher risk for serious complications from the pandemic virus. Pandemics are, fortunately, rare but can have devastating effects as was seen during the 1918-19 influenza pandemic when an estimated 50-100 million people died worldwide.1

The Community Preventive Services
In such instances, the evidence suggests that the benefits of school closures – reducing or delaying the spread of influenza within the schools and community – would outweigh the social and economic costs of closure. The task force did not recommend school dismissals in the event of pandemics with moderate to low rates of severe illness due to insufficient evidence or the expected costs outweighing benefits. Public support for prolonged school closures would likely be lacking in the case of less severe
A retrospective analysis of responses in 1918-19 by 43 U.S. cities found that early implementation of mitigation strategies led to longer times to reach peak mortality and lower peak mortality.3 Delayed implementation led to worse outcomes.4 Computer modeling suggests closing schools by the time prevalence among students reaches about 2% offers greater benefit in reducing infection rates.5 Delaying implementation from 10 diagnosed cases in the community to 30 or 100 cases increased the infection rate from 2% to 5% and 13%, respectively, and prolonged the necessary duration of school closures.6

The duration of intervention is also relevant. During the 1918-19 pandemic, some cities saw secondary disease peaks when mitigation strategies were relaxed.3,4 Reimplementation brought attack rates back down. In one model, rescinding school closures at a threshold of 3 cases/7 days instead of 0/7 days prolonged the duration of the epidemic.6 Another model found it is reasonable to reopen schools when prevalence is less than 1% in children.5 The interventions may need to be sustained for several weeks to