Design and baseline description of an observational population-based cohort study on COVID-19 vaccine effectiveness in the Netherlands - The VAccine Study COvid-19 (VASCO)

Abstract

Abstract VAccine Study COvid-19 (VASCO) is a cohort study with 5-year follow-up to assess the real-world vaccine effectiveness (VE) of COVID-19 vaccines in the Netherlands. VASCO was initiated when COVID-19 vaccination was introduced in the Netherlands. The primary objective is to estimate vaccine-specific VE against symptomatic SARS-CoV-2 infection, overall and in four subpopulations defined by age and medical risk, at 9 months after study start when most participants would have accumulated at least 6 months of follow-up. Secondary objectives are to estimate VE by time since vaccination and by severity of SARS-CoV-2 infection. Between May and December 2021, 45,271 participants aged 18–85 years have been enrolled in VASCO. Participants were included irrespective of their COVID-19 vaccination status or intention to get vaccinated. At inclusion, at 6, 12, 24, 36, 48 and 60 months after inclusion, and at one month after primary vaccination, participants are asked to take a self-collected fingerprick blood sample at home. In the serum samples, nucleoprotein (N) and spike protein receptor binding domain (RBD)-specific antibody titers are assessed to determine vaccine response and prior SARS-CoV-2 infection(s), including prior asymptomatic infections. 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. The main aim of VASCO is to contribute to policy decision-making regarding future COVID-19 vaccination. Furthermore, VASCO provides an infrastructure to conduct substudies in response to unforeseen developments within the COVID-19 pandemic.