Study: Smoking increases risk of viral and respiratory infections, including Covid-19; supports tobacco control to curb disease

A new study shows that smoking increases the risk of viral infections and respiratory illnesses, including one type of the coronavirus, this supporting efforts to curb tobacco use as a way to thwart Covid-19.  

The University of California, Davis Comprehensive Cancer Center study, published in the Nicotine and Tobacco Research journal, found that current smokers have a 12% increased risk of a laboratory-confirmed viral infection and a 48% increased risk of being diagnosed with respiratory illnesses. These results did not vary by type of virus, including a coronavirus.

“Past research has shown that smoking increases the risk of Covid-19 disease severity, but the risk of infection had been less clear,” UC Davis tobacco researcher and lead author of the study Melanie Dove said in a news release. “Our study findings show smokers have an increased risk of viral infection, including a coronavirus and respiratory illness.”

In combination with past findings, the researchers note that findings from this study support "urgent recommendations to increase tobacco control efforts for countering Covid-19," says the release. 

These findings are especially important to Kentucky, where 23.4% of adults and the state continues to have some of the highest rates of new Covid-19 cases. For help to quit smoking, the state runs a  1-800-QUIT-NOW hotline that offers free tobacco cessation services. 

Data for the study came from a re-analysis of the British Cold Study, a 1986-1989 study that exposed 399 healthy adults to one of five "common cold" viruses, including a strain of the coronavirus that existed prior to the novel coronavirus that causes Covid-19. 

The data showed that current smokers had an increased risk of respiratory viral infection and illness, with no significant difference across the types of viruses. It also showed that the increased association for the mild, common coronavirus that they tested did not reach statistical significance, which the researchers  said was likely due to the small sample size.

"These findings are consistent with known harms caused by smoking to immune and respiratory defenses and some observational evidence of increased Covid-19 infection and disease progression in current smokers. . . . The relative risks from this study can provide an estimate of the strength of associations that can be used to guide tobacco control decisions," says the release. 

The researchers note that one of the  main limitations of this study is that the mild common coronavirus that they tested may have different biological and health effects than other coronaviruses, including the one that causes Covid-19, which means the the findings may not be generalizable to other coronaviruses.

“These findings may have implications for addressing tobacco use at the population level as a strategy for preventing Covid-19 infection,” Elisa Tong, senior author and UC Davis internal medicine professor, says in the release.