Israeli study claims vaccines cut infection risk even in COVID-afflicted homes

Research was conducted before Delta variant, but deputy head of Sheba Medical Center, which took part in effort, calls findings ‘convincing illustration of vaccine effectiveness’

Nathan Jeffay is The Times of Israel's health and science correspondent

A health worker prepares a vaccination against COVID-19 at a vaccination center of the Tel Aviv municipality and Magen David Adom, in Tel Aviv, July 4, 2021. (Tomer Neuberg/Flash90)
A health worker prepares a vaccination against COVID-19 at a vaccination center of the Tel Aviv municipality and Magen David Adom, in Tel Aviv, July 4, 2021. (Tomer Neuberg/Flash90)

Israeli and French scientists say a study has found that COVID-19 vaccines are effective in even the most challenging of environments: a household where there is an infected person.

The chance of each household member getting infected shrunk from 57 percent without vaccine protection to just 4% when all those involved had received two doses of the vaccine, the authors of the study said Monday. The study only looked at recipients of the Pfizer-BioNTech vaccine.

“There is no more convincing illustration of vaccine effectiveness than this,” said Prof. Arnon Afek, deputy director of Sheba Medical Center, which conducted the research in collaboration with the Pasteur Institute and Sorbonne Université, both in France. Among the bodies funding the study were two French insurance giants: AXA and Groupama.

The study, which has been posted online but not yet peer reviewed, involved 215 people who were infected between December and April, and tracked patterns in their households with daily swab tests over a week and a half.

When an unvaccinated person was infected, an unvaccinated family member stood a 57% chance of catching the virus.

The strongest risk reduction, to a 4% chance of infection, happened when both the infected person and their relation were vaccinated. But even when just one party was vaccinated, the risk reduction was significant.

A young Israeli receives a COVID-19 vaccine injection, at Amal high school in the southern Israeli city of Beer Sheva, March 17, 2021. (Flash90)

When the sick person was unvaccinated but their relative was vaccinated, an unvaccinated family member stood a 17% chance of getting infected. When a vaccinated person got sick, an unvaccinated person had a 20% chance of infection.

Prof. Arnon Afek of Sheba Medical Center (Shai Pereg)

“The findings are clear, and very important — vaccinated people get infected less, and infect less,” Afek told The Times of Israel.

The study was conducted at a time when the Alpha coronavirus variant, which originated in Britain, was rampant. Today, it is the Delta variant that is wreaking havoc and showing itself able to penetrate some vaccine defenses and infect and be spread by those who have been vaccinated.

“We don’t yet have similar research for the Delta variant, but still, these remain important findings because they give an insight in to how the vaccine can perform,” said Afek.

Gili Regev-Yochay, director of Sheba’s Infectious Disease Epidemiology Unit and head researcher in the study, said that the results are important in underscoring that vaccines don’t only protect recipients from infection, but make them less infectious to others if they do nevertheless catch the coronavirus.

“The findings of this study reinforce findings from previous studies conducted at Sheba, which indicate that vaccinated people are not only less infected but also less contagious,” she said.

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