Before children were authorized to receive the Pfizer-BioNTech vaccine, living with 1-2 fully vaccinated parents significantly reduced children’s risk of COVID-19 infection during the Alpha and Delta periods.
The Pfizer-BioNTech (BNT162b2) vaccine is now approved and recommended for children 5 years and older. However, the Emergency Use Authorization (EUA) of the Pfizer-BioNTech vaccine for young children came after Delta became the dominant COVID-19 variant worldwide.
One study, published in yesterday in Science, found that parental vaccination with the Pfizer-BioNTech vaccine offered children indirect protection against COVID-19 infection and disease. The study, conducted by the Clalit Research Institute, Harvard University, and Tel-Aviv University, analyzed data records to examine how vaccination of Israeli parents served to benefit children as well.
The investigators utilized data compiled by Israel’s largest healthcare to estimate Pfizer-BioNTech’s indirect vaccine efficacy. They conducted their analysis from January 17, 2021-March 28, 2021 (when the Alpha variant was dominant) and July 11, 2021-September 30, 2021 (when the Delta variant was dominant).
The first period of the study included 400733 children and adolescents from 155305 distinct households who combined for 2116306 person-weeks of follow-up. The average age of the children was 6 years, and 52% were male. The second period of the study included 181307 unvaccinated children from 76621 distinct households who offered a combined 1089191 person-weeks of follow-up. The average age during the latter study was 5, and 52% of the children were male.
During the early (Alpha) period, a single vaccinated parent offered a 26% reduced risk of COVID-19 infection for children living in the same household, while having 2 vaccinated parents was associated with a 71.7% decreased risk of infection. The investigators found this result to be fairly consistent across age groups and household sizes.
During the late (Delta) period, investigators compared parents vaccinated with a third, “booster” Pfizer-BioNTech vaccine to those who had only received 2 doses 5 or more months prior. A single boosted parent was associated with a 20.8% risk reduction for cohabitating children, and 2 boosted parents offered a 58.1% reduced risk of infection. For the later Delta period of the study, vaccine efficacy was slightly lower for older children (7-11 years) than younger children (0-2 years).
For fully vaccinated adults, the direct efficacy of Pfizer-BioNTech mRNA COVID-19 vaccination was estimated to be 94.4% during the Alpha period and 86.3% during the Delta period. Full vaccination of an infected parent was associated with a 72.1% decreased chance of infection of one or more susceptible children in the household during the Alpha period, and a 79.6% reduced risk of transmission during the Delta period.
“Vaccination not only provides direct protection, it also provides indirect protection to unvaccinated individuals living with the vaccinated individuals in the same household. This study highlights the indirect protection provided by vaccinated parents to their unvaccinated children, irrespective of household size or the child’s age, for both the Alpha and the Delta variants,” said Dr. Samah Hayek, a senior investigator at Clalit Research Institute.