A research study on climate change and influenza, the findings of which were recently published in PLOS Currents (www.plos.org), posits that “warm winters are more likely to be succeeded by early and severe influenza seasons due to fewer people being infected due to the warm weather, thereby leaving an unnaturally large fraction of susceptible individuals in the population going into the next season.”
The following season could be worse, due to the earlier onset of flu season possibly occurring at a time when fewer people would have been vaccinated against that year’s strains.
Sherry Towers, a professor at Arizona State University, and her team, studied flu patterns and climate patterns in the United States from 1997 to 1998 to the present.
The study suggested that “when a winter was mild, on average 72 percent of the time the next epidemic was more severe than average, with epidemic growth rate 40 percent higher than average, and a peak timing occurring 11 days earlier than average. In addition, the relative likelihood of the following epidemic peaking before January 1st was over 80 percent higher.”
Influenza transmission is lower when conditions are warm or humid, and the winter of 2011-2012 was very warm, followed, predictably, according to the study, by a season with early onset and greater severity, which happened this year.
The influenza virus mutates constantly, thus each year a new vaccine is developed which produces immunity to only a few strains of the virus. This year, the vaccine is effective against A strains, but less so for B. Immunity produced by any flu vaccine lasts approximately a year, sometimes less, sometimes more. Next year, a quadrivalent vaccine is expected to be produced that will guard against four strains of the virus rather than two or three, but researchers are anxious for funding that would enable them to work on a universal flu vaccine that would be effective against thousands of strains.