Smoking associated with increased risk of COVID-19 symptoms

The study published today in Thorax, by researchers from King's College London, investigates the association between smoking and the severity of the COVID-19.

Researchers analysed data from the ZOE COVID Symptom Study App. Of the participants of the app, 11% were smokers. This is a lower proportion than the overall UK population of 14.7%, however, it reflects the demographics of the self-selected sample of the ZOE COVID Symptom Study.

While more than a third of users reported not feeling physically well during the period of study (24th March and April 2020), current smokers were 14% more likely to develop the classic triad of symptoms suggesting diagnosis of COVID-19: fever, persistent cough and shortness of breath -- compared to non-smokers.

Current smokers were also more likely to have a higher symptom burden than non-smokers. Smokers were 29% more likely to report more than five symptoms associated with COVID-19 and 50% more likely to report more than ten, including loss of smell, skipping meals, diarrhoea, fatigue, confusion or muscle pain. A greater number of symptoms suggested more severe COVID-19.

Additionally, current smokers who tested positive for SARS-CoV-2 were more than twice as likely as non-smokers to attend hospital.

The researchers recommended that a smoking cessation strategy be included as an element to address COVID-19, as smoking increased both the likelihood of symptomatic disease and disease severity. Reduction in smoking rates could also reduce the health system burden from other smoking-related conditions that require hospitalisation.

Dr Mario Falchi, lead researcher and Senior Lecturer at King's College London said: "Some reports have suggested a protective effect of smoking on COVID-19 risk. However, studies in this area can easily be affected by biases in sampling, participation and response. Our results clearly show that smokers are at increased risk of suffering from a wider range of COVID-19 symptoms than non-smokers."

Claire Steves, lead researcher, consultant physician and Reader at King's College London, said: "As rates of COVID-19 continue to rise and the NHS edges towards capacity, it's important to do all we can to reduce its effects and find ways to reduce hospital admissions. Our analysis shows that smoking increases a person's likelihood to attend hospitals, so stopping smoking is one of the things we can do to reduce the health consequences of the disease."