It is important to note that during the study period, the alpha variant of the coronavirus was dominant in the Netherlands. But the researchers’ findings are expected to apply to the much more contagious delta variant to some extent as well.
Much smaller chance
The RIVM researchers looked at how often a fully vaccinated person infects other people within their own household. They compared that to how often unvaccinated people infect others within their own household.
Fully vaccinated people who became infected with the virus – despite a much smaller chance of contracting the virus – infected 11 percent of their housemates. Unvaccinated individuals who were themselves infected with SARS-CoV-2 transmitted it to 31 percent of their housemates.
Contamination within household
Adjusted for age, vaccination status of the housemates and for the month of the year, the scientists concluded that the chance of being infected within a household by a fully vaccinated person is 71 percent smaller than by an unvaccinated person. Within a household, exposure is high compared to many other situations.
The study ran from February to May of this year and is therefore about the alpha variant that was dominant at the time. The dataset contained more than 113,000 infectious persons and more than a quarter of a million documented contacts with housemates. Of the group of infectious people, 622 were fully vaccinated and more than two thousand were partially vaccinated.
Vaccinated housemates of infected persons were 75 percent less likely to become infected than unvaccinated housemates.
After partial vaccination of an infected person, he still transmits the virus to 29 percent of his housemates. One shot of the vaccine, of which two are needed, therefore hardly helps against transmission of the virus.
‘You really don’t just vaccinate yourself, but also for the people around you,’ says Brechje de Gier, principal researcher at RIVM. In RadiOlympia she tells more about the research.
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