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Scientists say it's reasonable to assume that smoking or vaping could make COVID-19 symptoms more severe once infected, according to Scientific American.

To be clear, a direct link has yet to be investigated by researchers — but there's plenty of evidence that smoking or vaping suppress immune function in the lungs and trigger inflammation.

Scientists have also found that more severe COVID-19 cases were associated with chronic lung conditions — which in turn is linked to smokers and vapers as well. Some preliminary studies in China have found links between more severe COVID-19 cases and a history of smoking, but it's too early to draw conclusions as many of them still await peer review.

"All these things make me believe that we are going to have more severe cases—especially [in] people who are [long-term] smokers or vapers," said Melodi Pirzada, chief of pediatric pulmonology at NYU Winthrop Hospital on Long Island, to Scientific American.

"There’s a very coordinated series of events that take place when you do become infected with a virus," associate professor of microbiology and immunology at the University of North Carolina Ray Pickles told Scientific American. "I think once you start perturbing this sequence of events in any which way or direction, that’s when things can go awry."

Scientists have found plenty of evidence for smoking being a risk factor for influenza. The link to vaping, however, is definitely less clear on the matter. Mice studies have found a link between e-cigarette aerosol lowering the chances of surviving influenza A, a common influenza virus.