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Researchers are learning how e-cigs can increase risk of flu infection. Getty Images
  • A new study in mice finds that vaping may impair how well the body responds to viral respiratory infections.
  • Cigarette smokers are more likely to catch the flu, but research is still ongoing for e-cigarette users.
  • Experts advise e-cigarette users get their flu shot in order to avoid infection.

Cigarette smokers are more likely to catch the flu and have more severe symptoms than nonsmokers.

But what about people who vape?

Widespread vaping has only been around for only about a decade, so there’s much less research on how well vapers get through flu season.

But recent mouse and other studies suggest that e-cigarette vapor can impair the lungs’ natural ability to fight viral infections like the flu. This may worsen symptoms and increase the risk of complications.

In a recent study, researchers from the Baylor College of Medicine in Houston found that mice who were chronically exposed to e-cigarette vapor — even nicotine-free vapor — responded poorly to the influenza virus.

“These mice were not able to handle even a small dose of the virus. A large number of the mice succumbed to their infection,” said study author Dr. Farrah Kheradmand, a pulmonologist and professor of medicine at Baylor College of Medicine in Houston.

“Those that did survive had a very profound inflammatory response in their lungs,” she added. “Even 2 weeks after the virus was cleared from their body, their lungs still looked very abnormal.”

Mice that were not exposed to e-cigarette vapor became a little sick from the flu virus, but they recovered more quickly.

The results of the study were published last month in The Journal of Clinical Investigation.

Mice in this study were exposed to e-cigarette vapor for 3 to 4 months — this is equivalent to a person vaping from about their teenage years until some time in their 50s.

But other research has shown that even just 2 weeks of exposure to e-cigarette vapor can impair how well mice respond to the flu virus.

Kheradmand’s research also showed that e-cigarette vapor affected the lung macrophages, immune cells that clear the airways of infectious, toxic, or harmful particles.

In mice exposed to e-cigarette vapor, the lung macrophages had an abnormal buildup of lipids, or fats.

This type of lipid buildup has shown up in some of the recent vaping-related illnesses. Some evidence suggests it is the result of oil in the e-liquids.

But Kheradmand said their data suggest that the lipids are not from e-cigarette liquids, but are from an abnormal turnover of the protective mucus layer in the lungs.

The mucus layer traps viruses and bacteria, which allows the immune system to eliminate them.

While this study was on mice and not humans, it’s not yet possible to say how this process affects human lungs. But Kheradmand said these early findings are worrying.

Together, these lung changes are “two strikes against people who are vaping,” said Kheradmand, in terms of how well their body handles the flu.

While that study was in mice, early research into vaping has shown how e-cigarettes can damage lung tissue in humans.

Other research has found that e-cigarette vapor can impair the lungs’ infection-fighting mechanisms — including removal of pathogens that get trapped in the mucus layer of the lungs.

Cells that line the airways have hair-like cilia that push mucus out of the lungs like an escalator, where it is cleared by coughing.

Research shows that vaping can impair the function of these cilia and reduce a person’s cough sensitivity. The decreased cough reflex can happen after just 30 puffs on an e-cigarette.

Ilona Jaspers, PhD, a professor of pediatrics, microbiology and immunology, and environmental sciences and engineering, at University of North Carolina at Chapel Hill, said vaping can also affect the immune response needed to fight a flu infection.

“We and others have found that vaping causes a general immune suppression marked by suppressed immune cell function and gene expression changes that are consistent with decreased overall immune responsiveness,” said Jaspers.

Vaping may also make the barrier formed by epithelial cells that line the airways more “leaky.”

In one laboratory study, researchers found that this happened when human lung epithelial cells were exposed to e-cigarette vapor for only 15 minutes a day for 2 to 5 days.

This could enable bacteria to get into the lung tissue or the bloodstream. Although the flu is caused by a virus, bacterial pneumonia is a potential complication of the flu.

One caveat is that a lot of this reserach has been done in cultured lung or tissue cells, or in mice.

But Kheradmand thinks there’s little reason to doubt that what we see in mice wouldn’t also occur in people, because “most of the immune responses to viruses and bacterial pathogens are very similar among mammals.”

The body’s immune response is similar for other respiratory viruses, including the common cold. So vaping may also affect how well people respond to those, as well.

But more research is needed to verify these early findings.

“We need additional studies and collection of population data to make a stronger link between vaping and viral infections,” said Jaspers.

These kinds of studies have already been done in cigarette smokers, such as comparing their rates of flu to those of nonsmokers. So far no data like this is available on vapers.

Jaspers thinks the risks for people who vape are real enough that doctors should always ask people coming in with flu symptoms whether they vape.

The Centers for Disease Control and Prevention also recommends that everyone 6 months and older get an annual flu shot.

But Kheradmand strongly suggests that people who vape get vaccinated, because the changes in their lungs may put them at greater risk of complications.