David J.D. Earn, PhD; Daihai He, PhD; Mark B. Loeb, MD, MSc; Kevin Fonseca, PhD; Bonita E. Lee, MD, MSc; Jonathan Dushoff, PhD
Control of pandemic influenza by social-distancing measures, such as school closures, is a controversial aspect of pandemic planning. However, investigations of the extent to which these measures actually affect the progression of a pandemic have been limited.
To examine correlations between the incidence of pandemic H1N1 (pH1N1) influenza in Alberta, Canada, in 2009 and school closures or weather changes, and to estimate the effects of school closures and weather changes on pH1N1 transmission.
Mathematical transmission models were fit to data that compared the pattern of confirmed pH1N1 cases with the school calendar and weather patterns.
Alberta, Canada, from 19 April 2009 to 2 January 2010.
2009 virologic test results, 2006 census data, 2009 daily temperature and humidity data, and 2009 school calendars.
Age-specific daily counts of positive results for pH1N1 from the complete database of 35 510 specimens submitted to the Alberta Provincial Laboratory for Public Health for virologic testing from 19 April 2009 to 2 January 2010.
The ending and restarting of school terms had a major effect in attenuating the first wave and starting the second wave of pandemic influenza cases. Mathematical models suggested that school closure reduced transmission among school-age children by more than 50% and that this was a key factor in interrupting transmission. The models also indicated that seasonal changes in weather had a significant effect on the temporal pattern of the epidemic.
Data probably represent a small sample of all viral infections. The mathematical models make simplifying assumptions in order to make simulations and analysis feasible.
Analysis of data from unrestricted virologic testing during an influenza pandemic provides compelling evidence that closing schools can have dramatic effects on transmission of pandemic influenza. School closure seems to be an effective strategy for slowing the spread of pandemic influenza in countries with social contact networks similar to those in Canada.
Canadian Institutes of Health Research, Natural Sciences and Engineering Research Council of Canada, and Public Health Agency of Canada.
Whether schools should close during influenza epidemics is controversial. In 2009, testing for influenza A(H1N1) was performed for many months in Alberta, Canada. A mathematical model of H1N1 transmission was then constructed by using those virologic data, as well as census data, climate records, and school calendars.
School closure was associated with reduced transmission among schoolchildren by more than 50%, attenuating the first wave of the H1N1 epidemic. The reopening of the schools probably initiated the second H1N1 influenza wave. Seasonal changes in weather also affected the epidemic pattern.
Mathematical models simplify reality.
Closing schools may slow the spread of influenza epidemics.
Dates when schools closed and opened are indicated in blue. Classes ended on different dates for different levels of school: high school (grades 10 to 12) on 12 June, middle school (grades 7 to 9) on 22 June, elementary school (kindergarten [K] to grade 6) on 26 June, and junior kindergarten (JK) on 19 June; classes began on 27 August 2009 in Calgary and on 31 August 2009 in the rest of the province (Field Services, Alberta Ministry of Education. Personal communication.). The dotted line in each panel indicates the start of restricted testing on 30 October 2009 5. pH1N1 = pandemic H1N1 influenza. Top. Aggregate weekly total number of specimens tested, specimens positive for pH1N1 (red), and specimens positive for any type of influenza A or B, by date of specimen collection. The 2 highest peaks in the weekly totals, which are too high to be seen in the graph, are 2162 on 3 May 2009 and 3600 on 1 November 2009. Middle. Confirmed cases of pH1N1 broken into 2 age classes, school-age children (aged 5–18 y) and all others (children aged <5 y and adults aged >18 y). Bottom. Intensity plot of date of sample collection versus age of patient, with cumulative cases by age shown in the bar plot on the right.
pH1N1 = pandemic H1N1 influenza. Bottom left. Cumulative incidence by location (larger disks indicate more confirmed cases). Bottom right. Epidemic progression, aggregated by latitude. The cities and towns labeled on the right (with their population sizes) are also highlighted at their exact position in the left panel. Top right. Weekly confirmed cases in Calgary and Edmonton.
Box plots are based on 1000 realizations of our best-fit model, as specified in the 5. Data and simulation results are shown for school-age children (aged 5–18 y) (left panels) and for the rest of the population (right panels). Data are compared with simulations of our best-fit model (5) (top panels) and with predicted results if schools had been left open in Alberta throughout the summer (bottom panels). pH1N1 = pandemic H1N1 influenza.
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Olivia R., Briffault, Student
Hunter College High School
February 13, 2012
School Session Status and the 2009 H1N1 Pandemic
The results of this (Earn et al) paper confirm the results of earlier studies that exploited the substantial variation in school summer vacation dates across the United States. Chao et al. 2010 examined the relationship between H1N1 and the end of school summer vacation in the US and finds influenza rates were significantly higher after schools reopened in the fall. In a similar study, I found that influenza rates are about 1.7 times higher when children were in school than when they were not. The results were stronger for school closing in the spring than school reopening in the fall.
Chao DL, Halloran ME, Longini IM, Jr. School opening dates predict pandemic influenza A(H1N1) outbreaks in the United States. J Infect Dis 2010;202(6):877-80.
Briffault, Olivia. Weekly influenza-like-Illness rates were significantly lower in areas where schools were not in session in the United States during the 2009 H1N1 pandemic [Internet]. Version 14. PLoS Currents: Influenza. 2011 Mar 27 [revised 2011 Apr 27]:PMC3091530.
Earn DJ, He D, Loeb MB, Fonseca K, Lee BE, Dushoff J. Effects of School Closure on Incidence of Pandemic Influenza in Alberta, Canada. Ann Intern Med. 2012;156:173–181. doi: 10.7326/0003-4819-156-3-201202070-00005
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Published: Ann Intern Med. 2012;156(3):173-181.
Infectious Disease, Influenza.
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