The risk of becoming infected with the Delta variant and of transmitting the variant to other people is lower for vaccinated persons

A new study of infections with the Delta variant in Danish households shows that vaccines both protect against infection and against transmitting the virus to other persons.

Photo: Two syringes and three vials

The study examines how many persons in a household become infected if a member of the household has been infected with the coronavirus. The study includes 24.693 households with additionally 53.584 household members in the period June to October 2021, where the Delta variant was the dominant variant and where the epidemic was on a lower level.

The scientists found that vaccinated persons in the household had a lower risk of getting infected than unvaccinated persons. The overall vaccine effectiveness against infection was 61% compared to unvaccinated persons.

The research also shows that vaccinated persons who were infected had a lower risk of transmitting the virus to other household members than unvaccinated persons. The vaccine effectiveness against transmission was 42% compared to unvaccinated persons, the study found. The research does not include people who had been re-vaccinated.

Vaccinated persons have a lower viral load than unvaccinated persons

The study further examines the difference in the viral load amongst unvaccinated and vaccinated persons infected with the Delta variant. The results show that vaccinated persons, who are infected with SARS-CoV-2, generally have a lower viral load than unvaccinated persons.

“The viral load is generally lower in vaccinated persons with an infection than in unvaccinated persons, which is likely a reason for why vaccinated persons to a lesser degree transmit the virus to other household members. It is important that we now have knowledge that supports the fact that the vaccines not only protect you against becoming ill but also lower the risk of transmitting the virus considerably,” says doctor Camilla Holten Møller from SSI.

About the study

A new study by scientists at the University of Copenhagen and Statens Serum Institut (SSI) examines how well the vaccines protect against becoming infected and against transmitting the SARS-CoV-2 virus if you have become infected. The research, which has been published as a pre-print, is based on data from Danish households where at least one person has been infected with the Delta variant.

You can read the study here: Effect of Vaccination on Household Transmission of SARS-CoV-2 Delta VOC.