This is an observational study of participants in three general population health surveys (FinSote 2018, 2019, 2020) who are followed up until the incidence of SARS-CoV-2 infection or end of follow-up. The primary objective is to examine the association between tobacco use and the risk of SARS-CoV-2 infection in a general population sample in Finland.

Tobacco use, as a leading risk factor of death and disability due to respiratory diseases, was expected to increase the risk of SARS-CoV-2 infection and COVID-19 deaths. Earlier epidemiological studies, however, showed that smokers were underrepresented among patients hospitalized due to COVID-19. The most recent meta-analysis has confirmed these early findings, showing that current smokers had lower risk of SARS-CoV-2 infection than never smokers (Relative risk 0.71, 95% Credible interval 0.61; 0.82). A majority of these studies are based on samples of hospitalized patients, tested population or specific population groups, which might not represent the general population. In addition, data on tobacco use has been primarily collected from electronic health records or retrospectively and therefore prone to misclassification and information bias.

A message of a protective effect of tobacco use could undermine public health efforts to curb its use and reduce the perception of harm in the general population. Studies with general population samples and prospective data collection are thus urgently needed.

The aim of the study is to examine the association between tobacco use and the risk of SARS-CoV-2 infection. We will explore several forms of tobacco use (smoking, moist smokeless tobacco and e-cigarettes) and investigate whether introducing a potential collider bias by adjusting for mediating risk factors (alcohol use, physical activity and obesity) could have explained earlier results. We will use data from a prospective cohort study of nationally representative health surveys in Finland linked to SARS-CoV-2 incidence data, which is less subject to collider and recall bias than previous case-control studies.

Inclusion Criteria:

• Permanent residents of Finland
• Registered in the Population Register at the moment of sampling
• Aged 20 and over
• Participated in the FinSote surveys in 2018, 2019 or 2020

Exclusion Criteria:

• Temporary residents in Finland or tourists
• Age less than 20 years old
• Did not participate in FinSote surveys in 2018, 2019 and 2020

Permanent residents in Finland aged 20 and over who participated in the FinSote surveys in 2018, 2019 and 2020. These are general population samples representative of the Finnish population. The sampling frame was the Population Register (in 2020 the Digital and Population Data Services Agency, created after the merge between the Population Register of Statistics Finland and local register offices), which includes all individuals residing permanently in Finland, including conscripts and people living in institutions.

Researchers can access individual data by contacting the Responsible Researcher at the Finnish Institute for Health and Welfare, Suvi Parikka, suvi.parikka [at] thl.fi.

Information about FinSote surveys, including questionnaires, can be found in https://thl.fi/fi/tutkimus-ja-kehittaminen/tutkimukset-ja-hankkeet/finsote-tutkimus