Parental vaccination against COVID-19 confers substantial protection to children residing in the same household, according to a study that reinforces the importance of immunisation to curb the SARS-CoV-2 pandemic, and protect those who cannot be vaccinated.

A team of researchers from Harvard University, US, Clalit Research Institute and Tel-Aviv University in Israel, analysed one of the world’s largest integrated health record databases to examine the indirect protection provided to unvaccinated children.
The study, published in the journal Science on Thursday, shows that not only is a vaccinated parent less likely to experience a documented infection, they are also less likely to transmit the infection to other household members if infected.

“Vaccination not only provides direct protection, it also provides indirect protection to unvaccinated individuals living with the vaccinated individuals in the same household,” said Samah Hayek, senior researcher at Clalit Research Institute.

“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,” Hayek said.

Between June and October 2021, a wave of infections dominated by the Delta variant swept through Israel.

During this period, the researchers studied 181,307 unvaccinated children from 76,621 distinct households.

They compared parents vaccinated with a third dose of the Pfizer preventive to parents who received only two shots at least five months prior.

The study estimated that a single boosted parent decreased the risk of infection by 20.8 per cent, while two boosted parents decreased the risk for infection by 58.1 per cent.

The researchers also conducted a similar study during an earlier wave from December 2020 through March 2021, in which the Alpha variant was dominant.

During this period, they studied 400,733 unvaccinated children and adolescents from 155,305 distinct households.
They compared unvaccinated parents to those receiving two doses of the vaccine and found the indirect protection of parental vaccination on children to be even stronger.

The researchers found the indirect effects of parental vaccination to be fairly consistent across households of different sizes, and across different age groups of children.

This included the youngest age groups of 0-2 and 3-6 years old that are still ineligible for vaccination, they said.
“While the age range for vaccination continually expands, many children and adolescents remain unvaccinated for different reasons,” said Noam Barda, from Clalit Research Institute.

“The current study shows that parental vaccination confers substantial protection for children living in the same household, emphasising that vaccination not only protects vaccinated individuals, but also their loved ones,” Barda said.

These results reinforce the importance of increasing vaccine uptake among the vaccine-eligible population to curb the spread of the SARS-CoV-2 pandemic and protect those who cannot be vaccinated.

“This study of Clalit data suggests vaccinated and boosted parents provide impactful protection from Covid-19 to their unvaccinated children,” said Ran Balicer, Director of the Clalit Research Institute.

“By quantifying the indirect protection provided from vaccinated parents to unvaccinated children, several mechanisms of protection emerge, including lower transmission from vaccinated parents with a breakthrough infection to their unvaccinated children, as compared with unvaccinated parents,” Balicer added.