The link between mRNA-based COVID-19 vaccines and infection risk among vaccinated individuals and their unvaccinated family members has been assessed in a new study.
Findings show that indirect protection for unvaccinated family members builds slowly. Two weeks after the recipient's first dose, the spouses of vaccinated individuals showed 8.7% (95% CI: -28.9 to 35.4) fewer cases of coronavirus than the spouses of unvaccinated individuals.
Ten weeks after the first dose, the indirect effectiveness of vaccines for family members was up to 42.9% (95% CI: 22.3 to 58.1).
That being said, it is difficult to evaluate how effectively Covid-19 vaccines stop viral transmission, as only some infections come from family members,' says Mika Kortelainen, Professor of Health Economics at the University of Turku and Chief Researcher at the VATT Institute for Economic Research.
'Evaluating the indirect effectiveness of vaccines in a mass vaccination programme is methodologically one of the hardest types of studies to do.
We have succeeded in partially answering this question in terms of COVID-19 vaccines by linking several Finnish administrative datasets,' explains the head of the research group, Academy Research Fellow Lauri Sääksvuori, based at the Finnish Institute for Health and Welfare and the University of Turku.
The study focuses on healthcare workers as they were typically the only ones in their households to get a vaccination against coronavirus in Finland during the study period, January-March 2021.
Governments are hoping to lift COVID-19 restrictions as vaccination coverage increases. At the same time, many under-vaccinated countries and territories have yet to design and initiate their mass vaccination programs.
The study provide new knowledge on how vaccines affect infections among the unvaccinated, offering additional insight for decision-makers to design effective vaccination strategies, societal control measures and travel recommendations for vaccinated individuals.
'We plan to next evaluate the indirect protective effect of COVID-19 vaccines on unvaccinated children in the family,' says doctoral candidate Jussipekka Salo at the University of Helsinki, who is part of the same research group.
This study is based on work done by the health economics group of the Helsinki Graduate School of Economics (GSE) Situation Room, which provides real-time information for decision-makers.