COVID-19 vaccine effectiveness against SARS-CoV-2 infection and long-term symptoms: Insights from the VAccine Study COVID-19 (VASCO)

Abstract

Evaluation of COVID-19 vaccines post-introduction is of high importance to inform future COVID-19 vaccination policy. Shortly after the introduction of the first vaccines in the Netherlands, the VAccination Study COvid-19 (VASCO) was established for this purpose. This dissertation draws on this large observational study and focuses on the effectiveness of COVID-19 vaccination against SARS-CoV-2 infection and long-term symptoms. The first part examines the effectiveness of the primary vaccination series and various booster vaccinations against infection. It considers protection against different virus variants as well as changes in effectiveness over time. The results show that the primary vaccination series initially provided high protection against infection, but that this declined with the emergence of the Omicron variant. Booster vaccinations increased protection again, although the protection decreased within six months. The second part of the dissertation focuses on long-term symptoms following infection, namely fatigue and post-COVID condition. The analyses show that fatigue after an Omicron infection was mostly limited to the acute phase, whereas infections caused by the Delta variant were associated with more prolonged fatigue. Furthermore, the risk of post-COVID condition was low in this study, with only small differences between vaccinated and unvaccinated participants. In the discussion, methodological challenges inherent to observational research are addressed. The dissertation also provides recommendations for future research and discusses considerations for COVID-19 vaccination policy.