Fully-vaccinated people can pass on the Delta variant at home, including to other vaccinated people, a study finds - but unvaccinated people are still at most risk

An NHS COVID-19 vaccination center administers the Pfizer vaccine to a man. Hollie Adams/Getty Images
Real-world data has shown that even fully vaccinated individuals can pass the Delta variant at home.

The study authors stated that vaccines protect against severe COVID-19, but they don't prevent it from spreading completely.

Experts advised people to be vaccinated and to take extra precautions.

Real-world data suggests that even fully vaccinated individuals can contract the deadly Delta variant and transmit it to others at home. However, unvaccinated persons are most at risk.

The study was led by Imperial College London, and published in Lancet Infectious diseasess on Thursday. It identified 71 patients who had contracted COVID-19 from the Delta variant.

The study revealed that 25% of the fully vaccinated household contact of these people caught COVID-19 compared to 38% for their unvaccinated contacts.

Ajit Lalvani (chair in infectious diseases at Imperial College London) co-led the study and stated in a statement that vaccines "not enough" to prevent people from contracting the Delta variant of the disease and spreading it at their homes. He said that this is likely to happen in other indoor settings, where people spend prolonged periods of time together.

Anika Singanayagam (a researcher at Imperial College London) co-leads the study. She stated in a statement that it was essential for people who aren't vaccinated, who still face severe illness risk, to receive a COVID-19 shot. Official data indicates that around three quarters of all people in the UK have been fully vaccinated.

Singanayagam stated that people who have been fully vaccinated become more vulnerable to COVID-19 "within the first few months." She said that those who are offered a booster should do so immediately.

Singanayagam said that the study had provided "important insights" into the reasons why the Delta variant was causing high COVID-19 cases around the globe, even in countries with high vaccination rates.

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She stated that "continued public health and social precautions to prevent transmission remain important even for vaccinated individuals."

Peter Openshaw, a professor of experimental medicine at Imperial College London who was not involved in the research, stated in a statement that there is a good chance you won't get infected if your partner has COVID-19. Your chances of getting infected are also better if your vaccines have been renewed.

He said that if you want to avoid getting infected, you should still wear a mask, wash your hands, and use a disinfectant even if you've been vaccinated.

Associate professor of cellular microbiology, University of Reading Dr. Simon Clarke stated in a statement that vaccines "drive Down" COVID-19 infection, but are "not a magic bullet."

He said that infection in the community can be amplified through transmission at home. Clarke warned that it would be wrong to assume that only households are the source of transmission.

Researchers from Imperial College London, Manchester NHS Foundation Trust and the UK Health Security Agency used UK's central contact tracking system to identify 621 participants. They then tested them for COVID-19, regardless of their symptoms, using a laboratory test. 163 of the 621 participants had COVID-19 and 71 were due to the Delta variant.

According to the study authors, 54% of those infected by Delta were fully vaccinated; 32% were not vaccinated and 14% had received a single vaccine dose.

The researchers then examined the number of participants infected at home as well as the vaccination status of the people who were infected. The National Institute for Health Research funded the study that lasted from September 2020 to September 2021.

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