Vaccination against the flu is the best way to stop its spread, but a recent study suggests increasing air circulation and cleaning surfaces to remove the virus from the environment.

Influenza, or flu, viruses cause about 200,000 hospitalizations every year in the U.S. Annual seasonal vaccination is our best line of defense, but in recent years, it has become clear that mismatches in the vaccine can limit its effectiveness.

We study how the flu virus spreads between people. While we strongly encourage everyone to get the flu vaccine, the findings from our recent study on the stability of flu viruses in the air can provide useful information for parents, teachers and health care officials to limit the spread of flu in the community.

By employing simple strategies to reduce the amount of flu virus in our environment, we can decrease the number of infections every year.

How the flu spreads

Flu spreads through the community in three ways:

  1. Direct contact – when you shake hands with or otherwise touch an infected individual.
  2. Indirect contact – when the virus spreads via a contaminated surface like a door handle.
  3. Aerosols – when the virus is expelled into the air by coughing, sneezing or just exhaling and is then inhaled by a susceptible individual.

It is clear that all three routes promote the spread of flu each season, but the relative importance of each is still unknown.

Scientists have long believed that flu viruses in aerosols would be inactivated quickly at moderate and high humidity. However, we recently showed that human respiratory mucus protects flu viruses that are in aerosols and in droplets on a surface from decay regardless of the humidity.

In our studies, we sprayed flu viruses into a rotating drum to test whether they were still infectious after an hour at a wide range of different humidities. We found no loss in the amount of infectious virus at any humidity, which means that expelled aerosols containing flu viruses are stable in the air for at least one hour. Our other unpublished data suggest that flu viruses, in the presence of mucus, can persist on some surfaces for up to 16 hours with very little loss in infectivity. These data demonstrate that infectious flu viruses are highly stable in the indoor environment.

By employing simple strategies to reduce the amount of flu virus in our environment, we can decrease the number of infections every year.

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