Trajectories of Seroprevalence and Neutralizing Activity of Antibodies against SARS-CoV-2 in Southern Switzerland between July 2020 and July 2021: An Ongoing, Prospective Population-Based Cohort Study.

OBJECTIVES: The COVID-19 pandemic continues, and evidence on infection- and vaccine-induced immunity is key. We assessed COVID-19 immunity and the neutralizing antibody response to virus variants across age groups in the Swiss population. STUDY DESIGN: We conducted a cohort study in representative community-dwelling residents aged five years or older in southern Switzerland (total population 353,343), and we collected blood samples in July 2020 (in adults only, N = 646), November-December 2020 (N = 1457), and June-July 2021 (N = 885). METHODS: We used a previously validated Luminex assay to measure antibodies targeting the spike (S) and the nucleocapsid (N) proteins of the virus and a high-throughput cell-free neutralization assay optimized for multiple spike protein variants. We calculated seroprevalence with a Bayesian logistic regression model accounting for the population's sociodemographic structure and the test performance, and we compared the neutralizing activity between vaccinated and convalescent participants across virus variants. RESULTS: The overall seroprevalence was 7.8% (95% CI: 5.4-10.4) by July 2020 and 20.2% (16.4-24.4) by December 2020. By July 2021, the overall seroprevalence increased substantially to 72.5% (69.1-76.4), with the highest estimates of 95.6% (92.8-97.8) among older adults, who developed up to 10.3 more antibodies via vaccination than after infection compared to 3.7 times more in adults. The neutralizing activity was significantly higher for vaccine-induced than infection-induced antibodies for all virus variants (all p values < 0.037). CONCLUSIONS: Vaccination chiefly contributed to the reduction in immunonaive individuals, particularly those in older age groups. Our findings on the greater neutralizing activity of vaccine-induced antibodies than infection-induced antibodies are greatly informative for future vaccination campaigns.

Decision-making on COVID-19 vaccination: A qualitative study among health care and social workers caring for vulnerable individuals.

In January 2021, the Swiss government introduced the first COVID-19 vaccines and prioritized allocation to at-risk individuals and professionals working with them. Despite this opportunity, vaccine uptake among staff employed in retirement homes and institutes for people with disabilities was suboptimal. This study aimed to capture real-time decision-making about COVID-19 vaccine among staff employed in nursing homes and institutes for people with disabilities in Southern Switzerland. We conducted semi-structured phone-interviews with 25 staff employed in retirement homes and institutes for people with disabilities between February and May 2021, i.e., when participants had to decide whether they wanted to adhere to the priority vaccination programme. Among participants, 21 either signed up for the COVID-19 vaccination or were fully or partly vaccinated at the time of the interview. For most participants, the vaccination choice was a challenging process: information appeared to be lacking and conflicting; numerous moral principles were at stake and contradictory; the way vaccination was organized clashed with the health values to which respondents had been previously exposed; finally, the fear of discrimination for those who decided not to get vaccinated loomed over the vaccination choice. Participants decided for or against vaccination based on principles, traditions, emotions, and a reflexive assessment of the personal vs. collective benefit of the vaccination, the latter being the most common within the investigated sample. This study shows that deciding to get vaccinated against COVID-19 is a nuanced process and that individuals cannot simply be categorized as "novax" or "provax" based on their vaccination decision.