This is an observational study of participants in two general population health surveys (FinSote 2018 and 2020) who are followed up for their COVID-19 vaccinations or end of follow-up. The primary objective is to examine the association between tobacco use and COVID-19 vaccine uptake and between-dose spacing.

Most high income countries have rolled out COVID-19 vaccinations, with the promise of reducing incident COVID-19 infections and preventing hospitalizations and deaths. A high vaccination coverage is crucial for several reasons: (i) to reduce the number of new COVID-19 cases, (ii) to diminish selective pressures leading to the emergence of new variants of concern, (iii) to prevent severe COVID-19 outcomes, such as hospitalizations and deaths, and (iv) to potentially reduce the risk of post-acute COVID-19 symptoms.

Smokers are at higher risk of COVID-19 hospitalizations and deaths and might thus benefit greatly from high vaccination coverage. However, evidence suggests that they may be less likely to be vaccinated, as smokers are less likely to adhere to preventive measures in general and have lower adherence to other vaccines. Reports of a protective role of smoking on the risk of COVID-19 infection might have also reduced the perceived risks from being infected.

Evidence regarding tobacco use and COVID-19 vaccine hesitancy is mixed. Some studies have shown greater mistrust in COVID-19 vaccine benefits and greater vaccine hesitancy and lower vaccine acceptance compared to non-smokers, while other studies have reported no differences by smoking status or lower levels of vaccine hesitancy in smokers compared to non-smokers. Few studies have examined the relationship between tobacco use and vaccine uptake, showing that smokers had higher odds of being vaccinated. These studies, however, are not representative of the general population and relied on self-reported vaccination status, resulting in higher risk of selection and information bias.

The investigators will expand current knowledge by examining two forms of tobacco use in Finland -smoking and smokeless tobacco use (snus)- and by analysing the spacing between vaccine doses. The study will use data from nationally representative surveys in Finland linked to vaccination registries, which reduces the risk of selection and information bias.

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 or 2020
• Provided consent for register linkage

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
• Did not provide consent for register linkage

Permanent residents in Finland aged 20 and over who participated in the FinSote surveys in 2018 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