A study published in the Lancet has found that people who have been fully vaccinated against COVID-19 are just as likely as unvaccinated people to transmit the virus to household members.

Researchers from institutions, including Imperial College London and the UK Health Security Agency, analysed data from 204 household contacts of 138 people who were infected with the Delta variant.

These contacts were tested daily for 14 days and 53 ended up testing positive – 31 were fully vaccinated and 15 were unvaccinated.

The study suggests that a fully vaccinated contact has a 25% chance of getting infected from a positive household member while an unvaccinated contact has a 38% chance.

While the numbers don’t specify the severity of the infections, the study indicates that the vaccination status of an individual doesn’t make much difference to how infectious they are to their household contacts.

Researchers said that their findings show how important vaccination is, as unvaccinated people cannot rely on the vaccination status of people around them to reduce their own risk of infection.

“The ongoing transmission we are seeing between vaccinated people makes it essential for unvaccinated people to get vaccinated to protect themselves from acquiring infection and severe Covid-19, especially as more people will be spending time inside in close proximity during the winter months,” Prof Ajit Lalvani of Imperial College London, UK, said.

“We found that susceptibility to infection increased already within a few months after the second vaccine dose – so those eligible for booster shots should get them promptly.”