Vaccine and Infectious Disease Division

School openings may have triggered 2009 novel H1N1 outbreak

t is well known that schools are breeding grounds for all kinds of communicable diseases, but scientific evidence of schools’ specific contributions to population-wide epidemics is often lacking.  The advent of novel H1N1 in the U.S. in late spring 2009 provided a unique opportunity for scientists to look at the effect of school openings in late summer 2009 on the spread of this flu strain, as infection levels remained relatively low over the summer.  VIDD staff scientist Dr. Dennis Chao, along with VIDD members Drs. Betz Halloran and Ira Longini, looked at data from the Centers for Disease Control and Prevention on doctor’s visits for influenza-like illness and from Google Flu Trends to get a picture of influenza spread in each U.S. state before and after schools opened.

 The researchers found that infections of pandemic H1N1 tended to increase dramatically two weeks following school opening dates in nearly all states.  In states with later opening dates, this lag time was slightly shorter, possibly due to changes in weather or to transmissions from neighboring states.  These results indicate that if there is threat of an influenza pandemic, as with the 2009 H1N1 epidemic, vaccination or other prevention strategies should be in place before schools open, or in worst-case scenarios, schools may choose to delay opening until vaccines are available.

Chao DL, Halloran ME, Longini IM Jr.  School opening dates predict pandemic influenza A(H1N1) outbreaks in the United States.  J Infect Dis. 2010 Sep 15;202(6):877-80.