Cohort profile: an observational population-based cohort study on COVID-19 vaccine effectiveness in the Netherlands – The VAccine Study COvid-19 (VASCO) (preprint)

ABSTRACT

Purpose - VAccine Study COvid-19 (VASCO) is a cohort study with 5-year follow-up that was initiated when COVID-19 vaccination was introduced in the Netherlands. The primary objective is to estimate real-world vaccine effectiveness (VE) of COVID-19 vaccines against SARS-CoV-2 infection in the Netherlands, overall and in four subpopulations defined by age and medical risk. Participants - The cohort consists of 45,547 community-dwelling participants aged 18-85 years who were included irrespective of their COVID-19 vaccination status or intention to get vaccinated. A medical risk condition is present in 4,289 (19.8%) of 21,679 18-59 year-olds and in 9,135 (38.3%) of 23,821 60-85 year-olds. After one year of follow-up, 5,502 participants had dropped out of the study. At inclusion, and several times after inclusion, participants are asked to take a self-collected fingerprick blood sample in which nucleoprotein and spike protein receptor binding domain-specific antibody titers are assessed. Participants are also asked to complete monthly digital questionnaires in the first year, and 3-monthly in years 2-5, including questions on sociodemographic factors, health status, COVID-19 vaccination, SARS-CoV-2-related symptoms and testing results, and behavioral responses to COVID-19 measures. Findings to date - VASCO data has been used to describe VE against SARS-CoV-2 infection of primary vaccination, first and second booster and bivalent boosters, the impact of hybrid immunity on SARS-CoV-2 infection and VE against infectiousness. Furthermore, data was used to describe antibody response following vaccination and breakthrough infections and to investigate the relation between antibody response and reactogenicity. Future plans - VASCO will be able to contribute to policy decision-making regarding future COVID-19 vaccination. Furthermore, VASCO provides an infrastructure to conduct further studies and to anticipate on changing vaccination campaigns and testing policy, and new virus variants. Registration - VASCO is registered in the online Dutch clinical trials register (trialsearch.who.int) with registration number NL9279.