This article is more than 5 years old. Information may no longer be current.
Flu season onset, severity tied to warm winters, climate change
Researchers reported on a pattern of warm winters that preceded spikes in US influenza activity during the next influenza season. The pattern was similar for influenza A and influenza B.
“From the standpoint of disease control, I think the most relevant aspect of our study is the conclusion that a mild influenza season during a mild winter is more likely than not to be followed by an earlier and more severe than average flu season,” study researcher Sherry Towers, PhD, of Arizona State University, told Infectious Disease News. “With this knowledge, public health authorities now have the potential to plan several months in advance for this likelihood by expediting the manufacture and distribution of influenza vaccines.”
Sherry Towers
The 2012-2013 influenza season, which got off to an early start, has been relatively severe, and influenza activity still remains elevated. According to the National Oceanic and Atmospheric Administration, the 2011-2012 winter was the fourth warmest recorded in the United States.
Towers and colleagues obtained data from the CDC on laboratory-confirmed influenza incidence across 10 US regions from the 1997-1998 to 2012-2013 influenza seasons. The researchers also took into account the antigenic characteristics of the dominant strains of that year and the accuracy of the vaccine match for each season.
A significant association was observed between the timing of the influenza season’s peak and epidemic growth rate when compared with the temperature and growth rate of the previous season. After a mild winter, the next influenza season was more severe than average 72% of the time, with an epidemic growth rate 40% higher than average and the season’s peak occurring 11 days earlier than average. The likelihood that the epidemic after a mild winter would peak before Jan. 1 was 80% higher.
“In the event of continued global warming, warm winters such as that of 2011-12 are expected to occur more frequently,” the researchers wrote. “Our results thus suggest that expedited manufacture and distribution of influenza vaccines after mild winters has the potential to mitigate the severity of future influenza epidemics.”
Disclosure: The researchers report no relevant financial disclosures.