Link between COVID vaccination and reduced household transmission,
Swedish study finds

Date:
October 11, 2021
Source:
Umea University
Summary:
People without immunity against COVID-19 were at considerably
lower risk of infection and hospitalization as the number of family
members with immunity from a previous infection or full vaccination
increased, according to a new study from Sweden.



FULL STORY ========================================================================== People without immunity against COVID-19 were at considerably lower risk
of infection and hospitalization as the number of family members with
immunity from a previous infection or full vaccination increased. This is
shown in a nationwide study performed by researchers at Umeaa University, Sweden.


==========================================================================
"The results strongly suggest that vaccination is important not only for individual protection, but also for reducing transmission, especially
within families, which is a high-risk environment for transmission," says
Peter Nordstro"m, professor of geriatric medicine at Umeaa University.

There is a vast body of research showing that vaccines strongly reduce
the risk of COVID-19. However, less is known about the influence of
vaccination on transmission of the virus in high-risk environments,
such as within families.

This is what researchers at Umeaa University aimed to investigate in a
new study.

In the study, the researchers found that there was a dose-response
association between the number of immune individuals in each family
and the risk of infection and hospitalization in non-immune family
members. Specifically, non- immune family members had a 45 to 97 per
cent lower risk of infection and hospitalization, as the number of immune family members increased.

The study is a nationwide, registry-based study of more than 1.8 million individuals from more than 800,000 families. The researchers combined
registry data from the Public Health Agency of Sweden, the National
Board of Health and Welfare, and from Statistics Sweden, which is the government agency that oversees statistical data. In the analysis, the researchers quantified the association between the number of family
members with immunity against COVID-19 and the risk of infection and hospitalization in nonimmune individuals. The researchers accounted for differences in age, socioeconomic status, clustering within families,
and several diagnoses previously identified as risk factors for COVID-19
in the Swedish population.

"It seems as if vaccination helps not only to reduce the individual's
risk of becoming infected, but also to reduce transmission, which in
turn minimizes not only the risk that more people become critically
il, but also that new problematic variants emerge and start to take
over. Consequently, ensuring that many people are vaccinated has
implications on a local, national, and global scale," says Marcel Ballin, doctoral student in geriatric medicine at Umeaa University and co-author
of the study.

========================================================================== Story Source: Materials provided by Umea_University. Original written
by Ola Nilsson. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Peter Nordstro"m, Marcel Ballin, Anna Nordstro"m. Association
Between
Risk of COVID-19 Infection in Nonimmune Individuals and COVID-19
Immunity in Their Family Members. JAMA Internal Medicine, Oct. 11,
2021; DOI: 10.1001/jamainternmed.2021.5814 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211011110812.htm

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