NARRATION: As the world confronts the Covid-19 pandemic, researchers have been focused on a curious statistic: the virus appears to kill more men than women and some fear smoking could be one of the reasons why.

ANNA SONG (DIRECTOR, NICOTINE AND CANNABIS POLICY CENTER, UNIVERSITY OF CALIFORNIA, MERCED: Why is it that you have more people surviving in South Korea than in Italy? In Korea smoking prevalence among women is very low, whereas in Italy, smoking prevalence is very high, particularly with men. Perhaps its not just gender. It may be behaviors namely smoking.

NARRATION: This observation is sparking research into Covid-19s impact on smokers and a new generation of vapers.

But, while that work is just beginning, scientists are racing toward discoveries. And University of California researcher Anna Song says that many of these will depend on scientific revelations from the past.

ANNA SONG: In this age of Covid, where things are happening so quickly and it is a new virus, there are lessons that weve learned through science.

NARRATION: Scientists have been studying the connection between smoking and the flu for decades and cell biologist Robert Tarran says the results are clear smokers are at much higher risk.

ROBERT TARRAN (PROFESSOR OF CELL BIOLOGY, UNIVERSITY OF NORTH CAROLINA, CHAPEL HILL): Smokers are about twice as likely to get influenza than non-smokers. And then if they get it, typically the outcome is a bit more severe. And the reason this happens, so normally your lung, it has multiple ways of getting rid of viruses and bacteria. So, it has all these natural antibiotics and natural ways of cleaning itself, which are just present and theyre working all the time just to try and help keep you healthy. But in smokers, all those processes dont work quite as well. So, theres more chance of viruses and bacteria getting into your deep lung.

ANNA SONG: Most people can fight off Covid. What they say is about 80 percent are able to feel like they have the flu, but theyll be OK. Where were getting into trouble is that it can lead to severe pulmonary distress. Smoking is a risk factor for having this disease progress, be incredibly severe, and lead to mortality, right is dying.

NARRATION: While Covid-19 is a new concern, smokings detrimental effects on health have long been well known.

ARCHIVAL(CBS, 1964):UNITED STATES SURGEON GENERAL: Cigarette smoking contributes substantially to mortality from specific diseases and to the overall death rate.

NARRATION: But vapers have countered that their habit is different. Sean Hannity is among those who recently went so far as to assert that vaping might help protect people from Covid-19. Theres little to back that claim.

ANNA SONG: There is no data to suggest that. There is no scientific evidence that vaping will protect you from Covid. In fact, as a scientist, I would hypothesize the opposite.

ROBERT TARRAN: When we first started doing vaping research, because theres a lot less chemicals in e-cigarettes compared to cigarettes, youd predict that it wouldnt have big of an effect on the body. But the studies weve done in the lungs, were seeing a lot of effects of vaping. And its just, you know, that goes back to the idea that biology, you cant always predict whats going to happen.

NARRATION: Tarran has been studying vaping since 2013 and the impact of a chemical they both have in common nicotine. One of the ways nicotine seems to harm the lung is by causing an over-production of enzymes, called proteases. These proteases are part of the lungs immune system, but too much is a bad thing. For instance, chronic elevations of them can lead to emphysema.

ROBERT TARRAN: Proteases are these, I always call them my molecular scissors. We found that vapers and smokers had similarly elevated levels of proteases in their lungs. We also found that it was actually the nicotine that was causing this.

NARRATION: George Mason University researchers Jim Olds and Nadine Kabbani say the bodys reaction to nicotine may be even more problematic with Covid-19 because of its close relationship to another coronavirus that swept through parts of the world in 2003 SARS .

ARCHIVAL (2003):NEWS REPORT: March 2003. Panic grips Hong Kong, as a deadly new virus sweeps through the city, one of the most densely populated in the world.

JIM OLDS (PROFESSOR OF NEUROSCIENCE), GEORGE MASON UNIVERSITY): So its a new virus. It shows up suddenly. It has a very high fatality rate. There is no treatment. SARS gains entry into lung epithelial cells in precisely the same manner that Covid-19 does. It binds to the very same protein. It enters those cells and then it wreaks havoc on those cells in the lung in a very similar manner. Therefore, what we learned clinically during SARS is relevant to what we are experiencing today.

NARRATION: One of those lessons? Nicotine can help these viruses find their way into healthy cells.

JIM OLDS: These lung epithelial cells, they have receptors for nicotine also. And what happens when these cells see nicotine, the virus sees more of its receptor and therefore theres a bigger target. Essentially, nicotine is acting to render those lung epithelial cells more vulnerable.

NADINE KABBANI (ASSOCIATE PROFESSOR OF SYSTEMS BIOLOGY, GEORGE MASON UNIVERSITY): A really alarming population is individuals who are actually vaping and using electronic cigarettes. The rates of vaping in young individuals are very high, so now were actually really concerned about this population.

ANNA SONG: The science on vaping is still relatively new But what is emerging is that it is not as safe as everyone assumed it to be. I would not be surprised if we start to see data on less desirable outcomes from Covid among vapers.

NARRATION: Even as scientists scramble to understand these connections, everyone from the FDA to New York Citys mayor is now raising the alarm.

ARCHIVAL (PRESS CONFERENCE, 3-8-20):MAYOR BILL DE BLASIO: If you are a smoker or a vaper that does make you more vulnerable If you are a smoker or a vaper this is a very good time to stop that habit and we will help you.