Weather patterns play significant role in seasonal flu

Hamilton, ON – Influenza is like a cloud, moving across Canada with the fall weather, McMaster University researchers have found.

They have established that the spread of seasonal flu in Canada is tied to low temperature and low humidity and travels west to east, findings that may have significant implications on prioritizing control measures such as the timing of introducing vaccination programs across the country.

The research coauthors were David Earn and Jonathan Dushoff, investigators with the Michael G. DeGroote Institute for Infectious Disease Research. Earn is also a professor of mathematics and statistics, and Dushoff, an associate professor of biology, both at McMaster. The study was led by DaiHai He while he was a postdoctoral researcher at McMaster. He is now a faculty member at Hong Kong Polytechnic University.

“We found that when there are lower temperatures and humidity in the autumn, the likelihood of an early seasonal influenza epidemic increases,” said Earn about the study published this week in the Proceedings of the Royal Society B.

“This is something public health officials might want to consider when determining the timing of a vaccination program. If you know you have low temperatures and humidity in the early autumn, our study suggests that it is more likely that you are going to have an earlier influenza epidemic, so there is greater value in vaccinating people earlier.”

The researchers studied cases of laboratory-confirmed influenza A in 10 Canadian provinces from October 1999 to August 2012. They found that, on average, the early emergence of seasonal flu cases across the country was correlated with low temperatures and low absolute humidity in the fall.  They also found a trend for the seasonal influenza to spread from west to east across Canada.

The report is tied to their other recent work that found closing elementary and secondary schools can help slow the spread of infectious disease and should be considered as a control measure during pandemic outbreaks.

“Because of these studies, we have a better understanding, and that allows us to conduct more accurate epidemic modeling,” said Earn. “While the biological mechanisms that connect weather to influenza transmission are not understood in detail, the correlations we found in this study have significant implications for epidemic prediction and control.”

The study received funding support from the Canadian Institutes for Health Research and National Sciences and Engineering Research Council of Canada.