Flu virus artwork

The influenza virus’s powers of infection are boosted by exposure to airway secretions. Credit: Roger Harris/SPL

Infection

A mucus wrapper helps flu to fly

The virus is vulnerable to moderate humidity without the protection of host secretions.

Phlegm and other airway secretions might help to protect airborne influenza-virus particles and facilitate the disease’s spread.

Previous research suggested that moderate humidity causes the influenza virus to decay. The finding has been cited to explain why flu outbreaks tend to occur in winter, when humidity is low. But the studies behind the finding did not look at the effects of mucus components on the fate of airborne viruses.

Seema Lakdawala at the University of Pittsburgh School of Medicine in Pennsylvania and her colleagues combined virus particles from the strain that caused the 2009 flu pandemic with secretions from human bronchial cells. The researchers then converted the mixture into an aerosol to mimic virus expelled by humans.

After one hour, these virus particles remained infectious at a variety of humidity levels, and showed little degradation. By contrast, virus particles aerosolized without the secretions decayed markedly at moderate humidity levels.