Recent findings on influenza and its link to seasonal changes has been published in the Journal of the Royal Society Interface.
The study was conducted by Linsey Marr and her colleagues at Virginia Tech University.
They measured the survival rate of influenza A virus in various humidity levels ranging from 17% – 100% and it was found that influenza virus A thrived better in high humidity environs especially during winters and rainy seasons.
The Study and Its Results
For the purpose of the study, scientists worked on mucus samples collected from volunteers. The flu virus was added to the human mucus and artificial respiratory fluid mimicking mucus. They then subjected these samples to varying levels of relative humidity from low and medium to high.
It was observed that at low humidity the respiratory droplets evaporated completely making it dry and hence convenient for the virus to survive. However, at moderate humidity, complete evaporation of the droplets does not occur leaving the virus ineffective for infection and exposed to higher chemical exposure.
In another study, samples were obtained from outpatients at a healthcare centre, a day care and 3 long duration flights. Even these showed similar results – that the virus was more viable in low humidity conditions than moderate and high humidity conditions.
The reason behind this is that cold air sucks out moisture from the respiratory fluids expelled into the air by coughs and sneezes which are infested with the virus from infected individuals. This makes the virus linger around suspended in the air for longer periods of time without perishing, until someone else inhales it.
This is the reason why flu is rampant during winter in most parts of the world including America. Similar are the reasons for Flu during rainy season in the tropics. When the relative humidity is 100 % outside, the composition of the respiratory droplets expelled into the air does not change. Hence it gets to live in conditions similar to that of the body. As the RH drops so does the droplet composition due to loss of water. This affects the viability of the virus.