Vaccination against SARS-CoV-2 infection among vulnerable and marginalised population groups in Denmark: A nationwide population-based study

Abstract

Background: Social deprivation, psychiatric and medical disorders have been associated with increased risk of infection and severe COVID-19-related health problems. We aimed to study the rates of SARS-CoV-2 vaccination in these high-risk groups.

Methods: Using health, vaccination, and administrative registers, we performed a population-based cohort study including all Danish residents aged at least 15 years, December 27, 2020, to October 15, 2021. Population groups were people experiencing: (1) homelessness, (2) imprisonment, (3) substance abuse, (4) severe mental illness, (5) supported psychiatric housing, (6) psychiatric admission, and (7) chronic medical condition. The outcome was vaccine uptake of two doses against SARS-CoV-2 infection. We calculated cumulative vaccine uptake and adjusted vaccination incidence rate ratios (IRRs) relative to the general population by sex and population group.

Findings: The cohort included 4,935,344 individuals, of whom 4,277,380 (86·7%) received two doses of vaccine. Lower cumulative vaccine uptake was found for all socially deprived and psychiatrically vulnerable population groups compared with the general population. Lowest uptake was found for people below 65 years experiencing homelessness (54·6%, 95% confidence interval (CI) 53·4-55·8, p<0·0001). After adjustment for age and calendar time, homelessness was associated with markedly lower rates of vaccine uptake (IRR 0·5, 95% CI 0·5-0·6 in males and 0·4, 0·4-0·5 in females) with similar results for imprisonment. Lower vaccine uptake was also found for most of the psychiatric groups with the lower IRR for substance abuse (IRR 0·7, 0·7-0·7 in males and 0·8, 0·8-0·8 in females). Individuals with new-onset severe mental illness and, especially, those in supported psychiatric housing and with chronic medical conditions had the highest vaccine uptake among the studied population groups.

Interpretation: Especially, socially deprived population groups, but also individuals with psychiatric vulnerability need higher priority in the implementation of the vaccination strategy to increase equity in immunization uptake.

Funding: Novo Nordisk Foundation.

Figure 1

Cumulative vaccine uptake by population groups in individuals aged 15-64 years, Dec 27, 2020 to Oct 15, 2021. The figures show the cumulative incidence functions of second dose of vaccine against SARS-CoV-2 infection by homelessness, imprisonment, substance abuse, severe mental illness, supported psychiatric housing, psychiatric admission, and chronic medical conditions compared with the non-exposed individuals from the general population (each comparison group excludes the specific exposed population group). The vaccines were offered at different points of time to different target populations. Older age-groups were prioritized in the vaccine rollout. The curves show the pattern of vaccine rollout for the specific population groups. Estimates at the end of follow-up, Oct 15, 2021, were used for comparison of the probability of second vaccine dose between groups, because all individuals aged 15 years and above had been invited for their second shot at that point. Competing risk from death and SARS-CoV-2 infection was considered in the analysis. The curves were smoothed to ensure anonymity of all individual cases.

Figure 2

Cumulative vaccine uptake by population groups in individuals aged 65+ years, Dec 27, 2020 to Oct 15, 2021. The figures show the cumulative incidence functions of second dose of vaccine against SARS-CoV-2 infection by homelessness, imprisonment, substance abuse, severe mental illness, supported psychiatric housing, psychiatric admission, and chronic medical conditions compared with the non-exposed individuals from the general population (each comparison group excludes the specific exposed population group). The vaccines were offered at different points of time to different target populations. Older age-groups were prioritized in the vaccine rollout. The curves show the pattern of vaccine rollout for the specific population groups. Estimates at the end of follow-up, Oct 15, 2021, were used for comparison of the probability of second vaccine dose between groups, because all individuals aged 15 years and above had been invited for their second shot at that point. Competing risk from death and SARS-CoV-2 infection was considered in the analysis. The curves were smoothed to ensure anonymity of all individual cases.