Why is flu worse in winter?

If you've ever wondered why flu is more common in winter a new study by researchers in the U.S. may have some answers to that question.

According to a team from Mount Sinai Medical College the flu virus is more stable and is airborne longer when the air is cold and dry i.e. during winter.

The researchers reached this conclusion after conducting a study using guinea pigs because the animal has been found to be good at spreading the influenza virus.

Lead author Dr. Peter Palese says the guinea pigs were exposed to the virus, then exposed to environments of varying controlled temperatures.

The experiment revealed that the spread of the virus was most prevalent at 41 degrees, and as the temperature rose, a decline in transmission was seen; at 86 degrees the virus stopped transmission completely.

The lower the temperature resulted in more days of the guinea pigs spreading the virus.

There have been a range of hypotheses put forward regarding the transmission of the influenza virus, including the decrease in the natural production of vitamin D or melatonin when days are shorter, resulting in lower immunity, as well as children at school, being more confined to indoor areas in winter weather.

This was thought to encourage transmission of the flu virus and this was then transferred home to their families.

Palese says the flu virus is more likely to be transmitted during winter on the way to the subway than in a warm room.

Dr. Palese is the chairman of the Mount Sinai Medical College's microbiology department and the study is published in PLoS Pathogens.