Mechanism For Seasonal Nature of Influenza
The exact mechanism behind the seasonal nature of influenza outbreaks is unclear. Some proposed explanations are:
- People are indoors more often during the winter, they are in close contact more often, and this promotes transmission from person to person.
- A seasonal decline in the amount of ultraviolet radiation may reduce the likelihood of the virus being damaged or killed by direct radiation damage or indirect effects (i. e. ozone concentration) increasing the probability of infection.
- Cold temperatures lead to drier air, which may dehydrate mucus membranes, preventing the body from effectively defending against respiratory virus infections. PMID 19204283
- The virus may linger longer on exposed surfaces (doorknobs, countertops, etc.) in colder temperatures.
- In nations where children do not go to school in the summer, there is a more pronounced beginning to flu season, coinciding with the start of public school. It is thought that the creche environment is perfect for the spread of illness.
- Vitamin D production from Ultraviolet-B in the skin changes with the seasons and affects the immune system.
Research in guinea pigs has shown that the aerosol transmission of the virus is enhanced when the air is cold and dry. The dependence on aridity appears to be due to degradation of the virus particles in moist air, while the dependence on cold appears to be due to infected hosts shedding the virus for a longer period of time. The researchers did not find that the cold impaired the immune response of the guinea pigs to the virus.
Recent research done by National Institute of Child Health and Human Development (NICHD) found that the influenza virus has a "butter-like coating". The coating melts when it enters the respiratory tract. In the winter, the coating becomes a hardened shell; therefore, it can survive in the cold weather similar to a spore. In the summer, the coating melts before the virus reaches the respiratory tract.
Read more about this topic: Flu Season
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