The indirect effect of mRNA-based COVID-19 vaccination on healthcare workers’ unvaccinated household members

Jussipekka Salo, Milla Hägg, Mika Kortelainen, Tuija Leino, Tanja Saxell, Markku Siikanen and Lauri Sääksvuori
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Jussipekka Salo: University of Helsinki
Milla Hägg: University of Helsinki
Tuija Leino: Finnish Institute for Health and Welfare
Tanja Saxell: VATT Institute for Economic Research
Markku Siikanen: VATT Institute for Economic Research

Nature Communications, 2022, vol. 13, issue 1, 1-7

Abstract: Abstract Mass vaccination is effective in reducing SARS-CoV-2 infections among vaccinated individuals. However, it remains unclear how effectively COVID-19 vaccines prevent people from spreading the virus to their close contacts. Using nationwide administrative datasets on SARS-CoV-2 infections, vaccination records, demographics, and unique household IDs, we conducted an observational cohort study to estimate the direct and indirect effectiveness of mRNA-based COVID-19 vaccines in reducing infections among vaccinated healthcare workers and their unvaccinated household members. Our estimates for adults imply indirect effectiveness of 39.1% (95% CI: −7.1% to 65.3%) two weeks and 39.0% (95% CI: 18.9% to 54.0%) eight weeks after the second dose. We find that the indirect effect of mRNA-based COVID-19 vaccines within households is smaller for unvaccinated children than for adults and statistically insignificant. Here, we show that mRNA-based COVID-19 vaccines are associated with a reduction in SARS-CoV-2 infections not only among vaccinated individuals but also among unvaccinated adult household members in a real-world setting.

Date: 2022
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DOI: 10.1038/s41467-022-28825-4

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