Smoking linked with increased risk of viral infection, coronavirus illness: Study

Los Angeles: Cigarette smoking is associated with an increased risk of viral infection, including a coronavirus and respiratory illness, according to a study.

The findings, published recently in the Nicotine and Tobacco Research journal, support urgent recommendations for doctors to help patients quit smoking as a way of countering COVID-19.

The researchers from the University of California (UC) - Davis found that current smokers have a 12 per cent increased risk of a laboratory-confirmed viral infection and a 48 per cent increased risk of being diagnosed with respiratory illnesses.

"Past research has shown that smoking increases the risk of COVID-19 disease severity, but the risk of infection had been less clear," said study lead author Melanie Dove from UC Davis.

"Our study findings show smokers have an increased risk of viral infection, including a coronavirus and respiratory illness," Dove said.

The researchers re-analysed data from the British Cold Study (BCS), a 1986-1989 challenge research that exposed 399 healthy adults to 1 of 5 "common cold" viruses.

This included a type of common coronavirus (coronavirus 229E) that existed prior to the novel coronavirus (SARS-CoV-2 virus), which causes COVID-19 disease.

The team calculated overall and coronavirus-specific unadjusted and adjusted relative risks for current smokers and each outcome, testing whether each association was modified by type of respiratory virus.

The study showed that current smokers had an increased risk of respiratory viral infection and illness, with no significant difference across the types of viruses.

The increased associations for only the coronavirus 229E did not reach statistical significance. This was likely due to the small sample size with only 55 participants, of whom 20 were smokers, they said.

These findings are consistent with known harms caused by smoking to immune and respiratory defences and some observational evidence of increased COVID-19 infection and disease progression in current smokers, the researchers said.

The researchers noted that one of the main limitations of this study is that the mild common coronavirus 229E may have different biological and health effects than other coronaviruses, including SARS-CoV-2.

Therefore, the findings may not be generalisable to other coronaviruses, they said.

"These findings may have implications for addressing tobacco use at the population level as a strategy for preventing COVID-19 infection," said senior study author Elisa Tong from UC Davis Department of Internal Medicine.