Why Flu Spreads in Winter

Flu Virus Spreads More Easily in Low Temperatures and Low Humidity

Medically Reviewed by Louise Chang, MD on October 19, 2007

Oct. 19, 2007 -- Winter is prime time for flu because of cold and dry conditions, a new study shows.

Researchers report that the flu virus spreads through the air more easily when the temperature and humidity are low.

They offer these tips to help curb the spread of the flu virus:

  • Set room air at warm temperatures (above 68 degrees Fahrenheit)
  • Keep rooms fairly humid (at least 50% humidity)

Anice Lowe, PhD, and colleagues at New York's Mount Sinai School of Medicine studied the flu virus in guinea pigs.

The scientists tweaked the temperature and humidity in the guinea pigs' cages.

The flu virus spread more easily through the air at 41 degrees Fahrenheit than at 68 degrees or 86 degrees.

In low humidity (relative humidity of 20% to 35%), the flu virus spread more easily through the air than when it was more humid.

The study appears in Public Library of Science Pathogens.

Got Your Flu Vaccine?

Getting a yearly flu vaccination is the single best way to protect against the flu, according to the CDC.

Flu season can start as early as October and last as late as May.

The best time to get vaccinated against the flu is October or November, but flu vaccinations can still be given in December or later, according to the CDC's web site.

The CDC recommends yearly flu vaccinations for the following groups of people:

  • Children aged 6 months to 5 years
  • Pregnant women
  • People aged 50 and older
  • People of any age with certain chronic medical conditions
  • People living in nursing homes or other long-term care facilities
  • People living with persons at high risk for flu complications
  • People living with or caring for children less than 6 months of age
  • Health care workers

Scientists remake flu vaccines every year based on the flu strains that they expect to be most prominent in the upcoming flu season. Don't rely on last year's flu vaccine to help you this year.

Show Sources

SOURCES: Lowen, A. Public Library of Science Pathogens, October 2007; vol 3. CDC: "Key Facts About Seasonal Flu Vaccine."

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