People without immunity to COVID-19 were at significantly lower risk of infection and hospitalization as the number of family members with immunity to previous infection or full vaccination increased. This is shown in a nationwide study carried out by researchers at Umeå University in Sweden.
The results strongly suggest that vaccinations are important not only for individual protection, but also for reducing transmission, especially within families, which are high-risk environments. “
Peter Nordström, Professor of Geriatric Medicine, Umeå University
There is plenty of research showing that vaccines greatly reduce the risk of COVID-19. However, less is known about the impact of vaccinations on the transmission of the virus in high-risk environments, such as within families. Researchers at Umeå University wanted to investigate this in a new study.
In the study, the researchers found that there was a dose-response relationship between the number of people immunized in each family and the risk of infection and hospitalization in non-immune family members. In particular, non-immune family members had a 45 to 97 percent lower risk of infection and hospitalization as the number of immunized family members increased.
The study is a nationwide, register-based study of more than 1.8 million people from more than 800,000 families. The researchers combined registry data from the Swedish Health Authority, the National Board of Health and Welfare, and Statistics Sweden, the government agency that monitors statistical data. In the analysis, researchers quantified the association between the number of family members with immunity to COVID-19 and the risk of infection and hospitalization in nonimmune individuals. The researchers took into account differences in age, socioeconomic status, clustering within families, and multiple diagnoses previously identified as risk factors for COVID-19 in the Swedish population.
“It seems that vaccination not only helps reduce the individual risk of infection, but also reduces transmission, which in turn not only minimizes the risk that more people will become critically ill, but also that new problematic variants will appear and begin So ensuring that many people are vaccinated has implications on a local, national and global level, “says Marcel Ballin, PhD student in geriatric medicine at Umeå University and co-author of the study.
Nordstrom, P., et al. (2021) Association between the risk of COVID-19 infection in nonimmune individuals and COVID-19 immunity in their family members. JAMA internal medicine. doi.org/10.1001/jamainternmed.2021.5814.