How Does Humidity Affect the Flu?
Most people consider the flu virus to be more predominant when the humidity is low. Is this really the case though? Two recent studies examined the effect that humidity has on the flu virus.
The first study, completed by the University of Pittsburgh School of Medicine, looked at how humidity levels affect the ability of the flu virus to be infectious. It is commonly thought that the virus would be less infectious at higher humidity levels. To test this theory, a rotating metal drum was designed that could keep aerosols suspended in the air, plus maintain consistent humidity levels. The drum was then fitted with filters to prevent any leakage.
During the testing process, human airway secretions were combined with H1N1 flu strain. Once aerosolized, the virus mixture was sprayed into the drum, which ran for 60 minutes. This is the average length of time that air will stay inside a building before spreading outside. The experiment was then repeated at seven different humidity levels. Different humidity levels were meant to mimic various environments ranging from rainy and tropical to dry and heated.
The results from this test showed that contrary to popular belief, the level of infectiousness didn’t change with humidity levels. In fact, it showed that the mucus and airway secretions expelled during coughing protect the virus while it’s airborne. Because of this protection, humidity does not affect how infectious the flu virus is to people.
While humidity may not affect the infectiousness of the flu, people still tend to get sick more often in cold environments with low humidity. A 2019 study by Yale University showed how low humidity affects a person’s immune system.
For the experiment, mice were genetically modified to resist viruses in the same way that humans do. Next, half the mice were placed in chambers with high humidity while the rest were in chambers with low humidity. Both chambers were kept at the same temperature. Once in the chambers, the mice were exposed to Influenza A virus.
The results showed that living in a low humidity environment did lower the immune response of the mice. This could be shown in three ways. First, it prevented the hairlike structures in airways, called cilia, from being able to remove the virus particles and mucus. Second, it hindered the ability of airway cells to repair any damage that was caused by the virus in the lungs. Finally, it prevented signaling proteins from alerting other cells of infection. The combination of these factors made the mice more likely to get sick while in a dry environment.
Both of these research studies provide a helpful look at the way humidity affects your likelihood of being sick. The flu virus may always be infectious, people are much more likely to get sick during low humidity when their bodies are less able to resist the virus.
University of Pittsburgh Schools of the Health Sciences. "Flu virus is protected by mucus when airborne, regardless of humidity." ScienceDaily. ScienceDaily, 7 June 2018.
Yale University. "Flu virus' best friend: Low humidity." ScienceDaily. ScienceDaily, 13 May 2019.