Why does influenza prefer cold weather?

We know that flu epidemics typically occur during the winter months. But why is that? A group of researchers seem to have found an explanation. They discovered that the influenza virus coats itself in a fatty substance that hardens in the cold to form a gel, offering a protective coating that allows it to spread from one individual to another. The shell thus created is so robust that it can even resist to certain detergents.

The outer membrane of the influenza virus is primarily composed of molecules from the lipid family, such as oils, fats and cholesterol. These researchers have observed that at temperatures slightly above the freezing point, the lipids that coat the virus solidify to a gel. As the temperature nears 16°C, the shell thaws progressively. Without its hard protective shell, the virus is incapable of surviving. However, when the virus succeeds in reaching the respiratory tract, the high temperature which prevails there melts the fatty capsule, allowing the virus to infect cells.

The researchers have come to the conclusion that spring and summer temperatures are actually too high to allow the viral membrane to attain its solid capsule form. In these temperatures, the researchers offer the hypothesis that the viruses weaken and dry out, which also coincides with the end of influenza’s intensely prolific period.

However interesting this new discovery may be, numerous questions remain to be answered. For example, it is unable to explain why certain influenza viruses actually thrive in tropical climates. It is thought that other undiscovered factors likely come into play to allow the spread of viruses

The researchers hope that their findings will nevertheless open new avenues of research for the treatment of winter influenza outbreaks.