Nordström P, Ballin M, Nordström A, et al. - Researchers examined the risk of COVID-19 in nonimmune individuals within families in correlation with the number of their family members with known immunity acquired from a prior COVID-19 infection or full vaccination (2 vaccine doses).

• Using data from nationwide registries in Sweden, researchers conducted a cohort study of 1,789,728 individuals from 814,806 families.

• Risk of contracting COVID-19 appeared 45% to 97% lower among family members without immunity as the number of immune family members increased.

• Overall, there appeared a key role of COVID-19 vaccines in lowering the transmission of the virus within families, which possibly has implications for herd immunity and pandemic control.