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One of the most contentious issues during the opening days and weeks of the 2009 novel H1N1 outbreak was the wisdom of closing schools to reduce transmission of the virus.
Since the virulence of the virus was largely unknown during those opening weeks, school closures were recommended by the CDC, and by other public health entities around the world.
The closing of schools, and other venues where people gather (sporting events, restaurants, shopping malls), has long been argued as being potentially an important mitigation strategy during a pandemic.
By early May (2009), however, it was apparent that the severity of this particular influenza virus was less than originally feared, and many public health agencies moderated their recommendations (see CDC No Longer Recommending School Closures For A/H1N1).
Some school districts, in the U.S., and elsewhere around the world, continued to close schools on a case-by-case basis well into the fall of 2009.
In a future, more severe pandemic, the extended closing of schools will once again likely be considered to help reduce the spread of the virus.
It isn’t an easy decision, however. School closings are controversial, and the issues are complex (see The Debate Over School Closures).
Critics point out that working parents rely on schools to watch their kids for much of the year during the day, and many low income families benefit from the school lunch program.
And of course, when schools are closed during a pandemic, some kids may congregate elsewhere and spread the virus anyway.
It is important, therefore, to get some idea of the benefits that school closings would generate. To that end we’ve seen several studies over the past two years that have produced varying estimates.
Study: Pandemic Mitigation by Early School Closure
Study: Student Behavior During Pandemic School Closings
School Closures Revisited
Study: Effect Of School Closures On Viral Transmission
Today we’ve a new study by the NIH’s Fogarty International Center, Arizona State University and colleagues at the Mexican Institute for Social Security that appears in PLoS Medicine that looks at the epidemiology of the H1N1 outbreak in Mexico, and the effects of school closings and social distancing on its transmission.
Our first stop are a few excerpts (slightly reformatted) from NIH press release, which summarizes this research article nicely.
Embargoed for Release
Tuesday, May 24, 2011
5 p.m. EDTMexican flu pandemic study supports social distancing
Fogarty research published in PLoS Medicine
Eighteen-day periods of mandatory school closures and other social distancing measures were associated with a 29 to 37 percent reduction in influenza transmission rates in Mexico during the 2009 pandemic. The research was carried out by scientists at the Fogarty International Center at the National Institutes of Health and published in PLoS Medicine.
The social distancing measures implemented by the Mexican health authorities in spring 2009 were effective in reducing disease transmission by more than one-third, the study found.
Social distancing interventions can be implemented during unusual infectious diseases outbreaks and include school closing, closure of movie theaters and restaurants, and the cancellation of large public gatherings. Mexico implemented a nationwide mandatory school closure policy during an 18-day period in late April and early May 2011.
The United States implemented school closure interventions on a local basis during the 2009 pandemic, but the impact of these interventions has yet to be evaluated.
During a particularly severe pandemic, it has been suggested that schools could be closed for up to 12 weeks. While drastic, that strategy is based – in part – on some of the experiences from the last great pandemic in 1918.
The chart above, taken from the PNAS journal article entitled Public Health Interventions and Pandemic Intensity During the 1918 Influenza Pandemic , shows the excess mortality in two American cities.
The tall spike represents Philadelphia, while the lower curve represents St. Louis.
Many researchers believe the startling difference in attack rates, and mortality, in these two cities can be explained by the way each city dealt with the outbreak.
In St. Louis, the Health Department closed public venues such as schools, theatres and churches very early in the outbreak, while Philadelphia did not.
While are societal costs to closing schools and other public venues, studies continue to show that during a severe pandemic it might very well be worth doing.
Here are some excerpts from the open access article in Plos Medicine. Follow the link to read it in its entirety.
Characterizing the Epidemiology of the 2009 Influenza A/H1N1 Pandemic in Mexico
Gerardo Chowell, Santiago Echevarría-Zuno Cécile Viboud, Lone Simonsen, James Tamerius, Mark A. Miller, Víctor H. Borja-Aburto
Abstract (Excerpts)
Background
Mexico's local and national authorities initiated an intense public health response during the early stages of the 2009 A/H1N1 pandemic. In this study we analyzed the epidemiological patterns of the pandemic during April–December 2009 in Mexico and evaluated the impact of nonmedical interventions, school cycles, and demographic factors on influenza transmission.
Methods and Findings
. . . We estimate that the 18-day period of mandatory school closures and other social distancing measures implemented in the greater Mexico City area was associated with a 29%–37% reduction in influenza transmission in spring 2009. In addition, an increase in R was observed in late May and early June in the southeast states, after mandatory school suspension resumed and before summer vacation started. State-specific fall pandemic waves began 2–5 weeks after school reopened for the fall term, coinciding with an age shift in influenza cases.
Conclusions
We documented three spatially heterogeneous waves of the 2009 A/H1N1 pandemic virus in Mexico, which were characterized by a relatively young age distribution of cases. Our study highlights the importance of school cycles on the transmission dynamics of this pandemic influenza strain and suggests that school closure and other mitigation measures could be useful to mitigate future influenza pandemics.
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