“I am a firm believer that one plus one equals two. Until I have the evidence to believe otherwise, I believe it is critically important for us to help people quit inhaling anything into their lungs that could be causing any type of inflammation, as the coronavirus will only find an inviting environment otherwise,” said Dr. Carolyn Dresler, a former associate director of medical and health sciences for the Center for Tobacco Products at the Food and Drug Administration, during a webinar last week for Action on Smoking and Health, an international nonprofit group.

A recent study in the New England Journal of Medicine found that Chinese coronavirus patients who smoked were more than twice as likely as those who didn’t to have severe infections from Covid-19. And smoking has been identified as a factor in patients who became ill in 2012 with MERS, another coronavirus.

Another signal points to the vulnerability of smokers to this coronavirus. The virus seems to attack the body by attaching to a binding receptor called angiotensin-converting enzyme-2, or ACE-2. Tobacco use may increase the expression of ACE-2. That is why doctors and researchers speculate that smokers may become infected with more copies of the virus than other patients.

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About 34 million adult Americans smoke cigarettes, according to recent data, and some five million middle- and high-school students report having vaped nicotine and marijuana products.

A frightening outbreak of life-threatening lung illnesses tied to vaping last summer was eventually tied to vaping marijuana oils that contained the additive vitamin E acetate. But doctors say at least 15 percent of the patients reported having vaped only nicotine products.

Dr. Winickoff, a pediatrician, said that prudence about marijuana products was also advisable: “Inhaling combusted or vaped cannabis products can damage lung cells, may increase viral replication, and does affect the ability to fight off infection,” he said.

“Clean air is what the lungs should be inhaling, especially during a global pandemic.”

Last month, the New York State Academy of Family Physicians called for a ban on sales of tobacco and e-cigarettes in the state during the pandemic. Already smoke shops are being shut down in many states because they are not deemed to be “essential” businesses. But some public health officials note that other retailers that sell cigarettes and vaping devices, such as gas stations and grocery stores, are still permitted to do so.