Objectives Seroprevalence studies to assess the spread of SARS-CoV-2 infection in the general population and subgroups are key for evaluating mitigation and vaccination policies and for understanding the spread of the disease both on the national level and for comparison with the international community. Methods Corona Immunitas is a research program of coordinated, population-based, seroprevalence studies implemented by Swiss School of Public Health (SSPH+). Over 28,340 participants, randomly selected and age-stratified, with some regional specificities will be included. Additional studies in vulnerable and highly exposed subpopulations are also planned. The studies will assess population immunological status during the pandemic. Results Phase one (first wave of pandemic) estimates from Geneva showed a steady increase in seroprevalence up to 10.8% (95% CI 8.2–13.9, n = 775) by May 9, 2020. Since June, Zurich, Lausanne, Basel City/Land, Ticino, and Fribourg recruited a total of 5973 participants for phase two thus far. Conclusions Corona Immunitas will generate reliable, comparable, and high-quality serological and epidemiological data with extensive coverage of Switzerland and of several subpopulations, informing health policies and decision making in both economic and societal sectors. ISRCTN Registry: https://www.isrctn.com/ISRCTN18181860.

Background Post COVID-19 condition (PCC) is an important complication of SARS-CoV-2 infection, affecting millions worldwide. This study aimed to evaluate the prevalence and severity of post COVID-19 condition (PCC) with novel SARS-CoV-2 variants and after prior vaccination. Methods We used pooled data from 1350 SARS-CoV-2-infected individuals from two representative population-based cohorts in Switzerland, diagnosed between Aug 5, 2020, and Feb 25, 2022. We descriptively analysed the prevalence and severity of PCC, defined as the presence and frequency of PCC-related symptoms six months after infection, among vaccinated and non-vaccinated individuals infected with Wildtype, Delta, and Omicron SARS-CoV-2. We used multivariable logistic regression models to assess the association and estimate the risk reduction of PCC after infection with newer variants and prior vaccination. We further assessed associations with the severity of PCC using multinomial logistic regression. To identify groups of individuals with similar symptom patterns and evaluate differences in the presentation of PCC across variants, we performed exploratory hierarchical cluster analyses. Results We found strong evidence that vaccinated individuals infected with Omicron had reduced odds of developing PCC compared to non-vaccinated Wildtype-infected individuals (odds ratio 0.42, 95% confidence interval 0.24–0.68). The odds among non-vaccinated individuals were similar after infection with Delta or Omicron compared to Wildtype SARS-CoV-2. We found no differences in PCC prevalence with respect to the number of received vaccine doses or timing of last vaccination. The prevalence of PCC-related symptoms among vaccinated, Omicron-infected individuals was lower across severity levels. In cluster analyses, we identified four clusters of diverse systemic, neurocognitive, cardiorespiratory, and musculoskeletal symptoms, with similar patterns across variants. Conclusion The risk of PCC appears to be lowered with infection by the Omicron variant and after prior vaccination. This evidence is crucial to guide future public health measures and vaccination strategies.

Functional immunity (defined here as serum neutralising capacity) critically contributes to conferring protection against SARS-CoV-2 infection and severe COVID-19. This cross-sectional analysis of a prospective, population-based cohort study included 1,894 randomly-selected 16 to 99-year-old participants from two Swiss cantons in March 2022. Of these, 97.6% (95% CI: 96.8–98.2%) had anti-spike IgG antibodies, and neutralising capacity was respectively observed for 94%, 92% and 88% against wild-type SARS-CoV-2, Delta and Omicron variants. Studying functional immunity to inform and monitor vaccination campaigns is crucial.

Introduction High participation in epidemiological studies is crucial for both external and internal validity. Because response rates have declined in recent years, there is an increasing need to understand the drivers and the barriers to research participation. This study aims to uncover the motivations in favour and against participation of older adults to an epidemiological study on health and dementia. Methods Twenty-two older adults, who already took part to the preliminary phase of an epidemiological study in Switzerland, agreed to participate to semi-structured, face-to- face interviews. An experienced researcher carried out all interviews in a quiet place of choice of the interviewee either at their domicile or the university, between November 2019 and January 2020. The interviews were audio and video taped, transcribed verbatim, and thematically analysed by two independent researchers. Results We identified three main themes for the motivations in favour of participation (i.e. personal, related to the outcomes of research, and altruistic motivations), and we highlighted subthemes for each theme (e.g. personal motivations: curiosity; civic engagement; interest in the topic; trust in science; everyone counts; openness; play the game). Motivations against participation reflected the first two themes, while there was no counterpart for altruistic motivations. Conclusions Our thematic analysis revealed that older adults hold specular motivations in favour and against participation to research. Studying jointly motivations in favour and against provides information for recruitment strategies and to overcome barriers to participation, respectively. Participatory action research can inform the design and conduction of and should precede epidemiological studies in older adults, and can potentially contribute to attain high response rates.

Objectives. Using longitudinal data from Southern Switzerland we assessed ten-month temporal trajectories of moderate-to-severe depression, anxiety and stress among adults after the first pandemic wave and explored differences between socio-demographic and health status groups. Study design. Population-based prospective cohort study. Methods. Participants were 732 (60% women) adults aged 20–64 who completed the Depression, Anxiety and Stress Scale on a monthly base since August 2020 until May 2021, as part of the Corona Immunitas Ticino study based on a probability sample of non-institutionalized residents in Ticino, Southern Switzerland. Results. Prevalence of moderate-to-severe depression increased from 7.5% in August 2020, to 12.5% in May 2021; anxiety increased from 4.8% to 8.1%; and stress increased from 5.5% to 8.8%. A steeper increase in poor mental health was observed between October 2020 and February 2021. Men had a lower risk for anxiety (OR = 0.58, 95%CI = 0.36–0.95) and stress (OR = 0.61, 95%CI = 0.44–0.95,) compared to women. Suffering from a chronic disease increased the risk for depression (OR = 1.82, 95%CI = 1.12–2.96), anxiety (OR = 2.38, 95%CI = 1.44–3.92) and stress (OR = 1.87, 95%CI = 1.14–3.08). The differences between these groups did not vary over time. Conclusions. In a representative Swiss adult sample, prevalence of moderate-to-severe depression, anxiety and stress almost doubled in the course of ten months following the end of the first pandemic wave in spring 2020. Women and participants with pre-existing chronic conditions were at higher risk of poor mental health.