Updated August 11, 2020

When someone’s lungs are exposed to flu or other infections the adverse effects of smoking or vaping are much more serious than among people who do not smoke or vape.

Smoking makes COVID worse if you get it and smoking -- and vaping -- increase the risk of being infected and developing COVID-19.

As of April 28, 2020 there were 19 peer reviewed papers that had data on smoking and COVID disease progression, 17 from China, 1 from Korea, and 1 from the US. Our peer reviewed meta-analysis of these 19 papers found that smoking was associated with more than a doubling of odds of disease progression in people who had already developed COVID.

There have been several reports, mostly in non-peer reviewed preprints, reporting lower levels of COVID-19 infections among smokers than nonsmokers. This is a surprising finding because, based on what we know about the effects of smoking and vaping on immune function of the respiratory system, one would expect that smoking and vaping would increase risks of COVID infection. A big problem with all the studies to date has been that they have been based on people who were tested, rather than samples drawn from the population as a whole. Because of limited availability of tests in many places, the resulting samples are biased toward people who may already have symptoms.

On August 11, 2020, Shivani Mathur Gaiha and Bonnie Halpern-Felsher from Stanford and Jing Cheng from UCSF addressed this problem in a study that used a population-based sample of youth and young adults, “Association between youth smoking, electronic cigarette use and Coronavirus Disease 2019. Among young people (ages 13-24) COVID-19 diagnosis was five times more likely among ever-users of e-cigarettes only, seven times more likely among ever-dual-users, and 6.8 times more likely among past 30-day dual-users.

These findings are particularly important as the case mix of people getting COVID is moving to younger people, perhaps reflecting increased exposures due to reduced social distancing and a lack of understanding about factors exacerbating COVID-related risk in this age group.

Why?

Smoking is associated with increased development of acute respiratory distress syndrome (ARDS) in people with a risk factor like severe infection, non-pulmonary sepsis (blood infection), or blunt trauma. People who have any cotinine (a metabolite of nicotine) in their bodies – even at the low levels associated with secondhand smoke – have substantially increased risk of acute respiratory failure from ARDS (paper 1, paper 2, paper 3).

The recent excellent summary of the evidence on the pulmonary effects of e-cigarettes reported multiple ways that e-cigarettes impair lungs’ ability to fight off infections:

Effects on immunity

Reporting of respiratory symptoms by e-cigarette users suggests increased susceptibility to and/or delayed recovery from respiratory infections. A study of 30 healthy non-smokers exposed to e-cigarette aerosol found decreased cough sensitivity.82 If human ciliary dysfunction is also negatively affected, as suggested by animal and cellular studies,83 the combination of reduced coughing and impaired mucociliary clearance may predispose users to increased rates of pneumonia. Exposure to e-cigarettes may also broadly suppress important capacities of the innate immune system. Nasal scrape biopsies from non-smokers, smokers, and vapers showed extensive immunosuppression at the gene level with e-cigarette use.84 Healthy non-smokers were exposed to e-cigarette aerosol, and bronchoalveolar lavage was obtained to study alveolar macrophages.46 The expression of more than 60 genes was altered in e-cigarette users’ alveolar macrophages two hours after just 20 puffs, including genes involved in inflammation. Neutrophil extracellular trap (NET) formation, or NETosis, is a mode of innate defense whereby neutrophils lyse DNA and release it into the extracellular environment to help to immobilize bacteria, a process that can also injure the lung.85 Neutrophils from chronic vapers have been found to have a greater propensity for NET formation than those from cigarette smokers or non-smokers.57 Given that e-cigarettes may also impair neutrophil phagocytosis,86 these data suggest that neutrophil function may be impaired in e-cigarette users. [emphasis added]

Studies in animals reinforce and help explain these human effects:

Two weeks of exposure to e-cigarette aerosol in mice decreased survival and increased pathogen load following inoculation with either Streptococcus pneumoniae or influenza A, two leading causes of pneumonia in humans.97 Furthermore, the aerosol exposure may lead to enhanced upper airway colonization with pathogens and to virulent changes in pathogen phenotype, as shown with Staphylococcus aureus.98 99 Thus, although more studies are needed, the animal data suggesting that vaping leads to an increased susceptibility to infection would seem to correlate with the population level data in young adult humans, whereby vapers have increased rates of symptoms of chronic bronchitis.23 [emphasis added]

A meta-analysis of the relationship between smoking and influenza found that smokers were more likely to be hospialized and admitted to the ICU.

The WHO has also concluded that, " smokers are more likely to develop severe disease with COVID-19, compared to non-smokers" and provides a nice discussion of how smoking increases risk of COVID-19 by increasing the risk of heart, lung, and other diseases.

Dr. Nora Volkow, director of the National Institute on Drug Abuse, posted an article on her blog "COVID-19: Potential Implications for Individuals with Substance Use Disorders," that stared off by saying

As people across the U.S. and the rest of the world contend with coronavirus disease 2019 (COVID-19), the research community should be alert to the possibility that it could hit some populations with substance use disorders (SUDs) particularly hard. Because it attacks the lungs, the coronavirus that causes COVID-19 could be an especially serious threat to those who smoke tobacco or marijuana or who vape.

She goes on to address other drug use and how COVID-19 could interact with them, including noting that

Vaping, like smoking, may also harm lung health. Whether it can lead to COPD is still unknown, but emerging evidence suggests that exposure to aerosols from e-cigarettes harms the cells of the lung and diminishes the ability to respond to infection. In one NIH-supported study, for instance, influenza virus-infected mice exposed to these aerosols had enhanced tissue damage and inflammation.

The whole blog post is worth reading.

In addition, an article in Scientific American, "Smoking or Vaping May Increase the Risk of a Severe Coronavirus Infection," summarizes how smoking and vaping affect the lungs and the immune system that is consistent with the view that using these products increases the risk of infection and worse outcomes. CNN also has a good story, "How smoking, vaping and drug use might increase risks from Covid-19." KQED/NPR reports on a young man who developed COVID that may have been aggrevated by his vaping. Fortunately, he recovered and has now stopped vaping.

The New York Times has a good story reporting that the Massachusetts AG put out an advisory urging people to stop smoking and vaping and pointed to resources to quit.

CDC, FDA, the Surgeon General, state health departments and everyone (including comedians, such as John Oliver who spent his whole show on the issue last weekend) working to educate the public on how to lower risk of serious complications from covid-19 should add stopping smoking, vaping, and avoiding secondhand exposure to their list of important preventive measures.

This would also be a good time for cities, states private employers and even individual families to strengthen their smokefree laws and policies – including e-cigarettes -- to protect nonsmokers from the effects of secondhand smoke and aerosol on their lungs and to create an environment that will help smokers quit.

The California Department of Public Health has information on smoking, vaping and COVID here, as does the California Smokers' Helpline. Trinity Health is also urging people to stop smoking to protect against COVID-19. FDA has said that vaping and smoking could increased COVID risks. CDC lists smoking as one of the risk factors for COVID-19 because smoking depresses immune function.

The Ontario Tobacco Research Unit has prepared a good two-page summary of the evidence and recommendations from various sources and authorities; it is available here. Tobacco Control also has a list of smoking and COVID resources here.

UCSF has added smoking and vaping nicotine and cannabis to COVID-19 triage protocol. Doing so will both improve patient care and, over the longer term, provide important information needed to quantfy how smoking and vaping impact COVID risks.

Who is challenging the evidence?

Not surprisingly, the pro-vaping lobbying organization CASAA does not agree with me or the other cited authorities; you can read their perspective here.

There has also been widespread press coverage of a couple papers suggesting that smoking and nicotine may be protective against COVID. The University of Bath released an excellent assessment of these studies describing their serious problems with these studies, including the fact that one isn't even a "study;" it's just a hypothesis. As they note, one of the authors also has longstanding ties to the tobacco industry. (The tobacco companies have a long history of promoting the idea that nicotine has health benefits [Study 1, Study 2].) Even if nicotine -- as hypothesized -- has some benefits, that is really different from cigarette smoke (or e-cigarette aerosol) which has thousands of other things in it. Those compounds likelyoverwhelm any "benefits" of nicotine. Salon.com also has an excellent article, "Here's how that rumor that smokers can't get COVID-19 got started." The title says it all.

More important, the August 11, 2020 paper that found a link between vaping and dual use of e-cigs and cigarettes and COVID infection avoids these problems by collecting data from a population-based sample rather than just people who are getting tested.

FREQUENTLY ASKED QUESTIONS

A lot of people have asked questions or sent comments on this post. I have responded to the people who asked unique questions. (I have not posted testimonials, offers of products, or questions for personal medical advice.) To present this material in a more accessible form, I organized these issues as a FAQ.

I will add to this as new issues come up.

I smoked for a long time before I quit. Are the risks still there?

The damage done to your respiratory system’s ability to fight infections starts recovering immediately after you stop smoking.

You are no longer bathing your lungs in toxic chemicals, so you are better off. The cilia (liitle hairs that move foriegn particles out of your lungs so you can cough them out) are recovering. CDC has a good summary of what happens after you quit, which is available here.

Will my lungs recover after I stop vaping?

While I have not seen similar studies for how quickly your respiratory tract recovers after you stop vaping, the same recovery likely happens after stopping smoking.

I quit smoking 2 months ago and am currently using 2 mg nicotine lozenges. Should I now also stop those because of the nicotine?

The effects of concern are due to the inhaled aerosol, not nicotine in your blood (which is what the NRT affects). You should eventually wean yourself off the NRT (because it has other effects), but I would stay on the NRT until you are sure that you are past smoking.

I recently quit Juuling and now am scared since I am using nicotine replacement therapy, patches or gum. Is the nicotine in them just as dangerous as the Juul?

You are much better off quitting Juul (or any other e-cigarette) than containing to vape. You are not inhaling the untrafine aerosol that Juul and other e-cigs -- and cigarettes -- deliver to your lungs.

Once you are sure you are de-addicted, you should get off the NRT, but stay on it as long as you need to avoid Juul. Counselling helps. State quitlines are available for free, which you can reach through 1-800-QUIT NOW. Many also provide medications to help when appropriate. Truth Initiative has a texting service targeted at Juul.

Does exhaled cigarette smoke spread corona virus?

This is not something that has received much study. The one study that looked at flu didn't find that smokers shed more virus. No one seems to have studied vaping.

Having said that, it is now clear that some of the coronavirus is in the exhaled aerosol, so the presence of the exhaled smoke or e-cigarette aerosol provides at least some indication of where the exhaled virus might be.

How do Juul e-cigarettes compare with other kinds of e-cigarettes in terms of infection risks?

As far as I know, no one has yet studied Juul particularly in terms of effects on pulmonary immunity and inflammation (although I have not done a comprehensive search). There is evidence that for vascular (blood vessel) effects, showing that Juul has the same adverse effects as an earlier generation e-cig or a Marlboro Red. Because, like all e-cigarettes and cigarettes, Juul delivers an aerosol of ultrafine particles and chemicals to your lungs, the safest thing would be to stop.

Because it uses nicotine salts, Juul and similar e-cigs appear to be more addictive than older e-cigs (and maybe even conventional cigarettes). I would seek help from your doctor or call your state quitline, which you can reach through 1-800-QUIT NOW. Many also provide medications to help when appropriate. Truth Initiative has a texting service targeted at Juul.

Health officials have said that people with existing conditions, including lung disease, are at increased risk, but have not, as far as I know, made any quantitative statements based on how severe the lung disease is.

Importantly, a study of youth and young adults found that vaping (without specifying the brand or device) is associated with increased risk of getting infected and developing COVID-19.

What about heated tobacco products, like Philip Morris' IQOS?

The evidence that Phillip Morris submitted to the FDA shows that, in terms of effects on lung function, inflammation, and immune surpression, IQOS is not detectably different from a cigarette. The details are available here.

Are the risks for COVID-19 associated with smoking or vaping cannabis?

The American Lung Association has a good summary of the evidence. Cannabis smoke is very similar to tobacco smoke (other than a different psychoactive agent, THC vs nicotine). And vaped cannabis delivers an aerosol of ultrafine particles and chemicals deep into the lungs too.

It would be sensible to stop using these cannabis products, too.

By the way, the federal government makes it almost impossible to study the cannabis products people are actually using. If I went down the street to a local cannabis dispensary and bought some products off the shelf and brought them back to UCSF to study, even in a chemistry lab, the federal government could pull all federal funding to all 10 UC campuses. This is a huge problem for scientists who are trying to get the answers to these reasonable questions that people are asking.

What about cannabis leaf vaporizers?

I haven't seen any direct evidence one way or the other in terms of pulmonary effects (although I didn't do an exhaustive search) of using a cannabis leaf vaporizer on pulmonary effects, but, like cigarettes and e-cigarettes, they develop an aerosol that you inhale. There is evidence that for vascular (blood vessel) effects, vaporizers have similar adverse effects as combusted marijuana smoke. All these different delivery modes -- smoking, vaping, vaporizers -- work by delivering an aerosol of ultrafine particles to your lungs to deliver the active ingredient (THC or nicotine). Those particles are not a good thing for your lungs (or your vascular system).

My advice: Don't put anything but air into your lungs.

What about using a cannibis bubbler to filter the flower?

It doesn't help. Studies of tobacco hookah shows that the particles and gases are carried through the water in the bubbles.