Why is winter the flu season?

According to researchers at the National Institute of Child Health and Human Development (NICHD) in the USA, influenza viruses are coated with a fatty protein - haemagglutinin - that protects the viruses against the cold. This fatty coating melts in the warmer respiratory tract, allowing the virus to infect cells.

In the summer, the higher temperatures quickly kill the viruses. According to Joshua Zimmerberg, the lead author of the study, the viruses can only infect cells when they are in this liquid phase.

These findings may lead to newer ways of treating flu, by interfering with the protective coat.