Double Vaccinated Three Times Less Likely to Test Positive for COVID-19

Investigators from the Imperial College London have found that individuals who have received 2 doses of a COVID-19 vaccine are 3 times less likely to test positive for the virus than those who are unvaccinated.

The findings come from the REACT-1 study, a major coronavirus monitoring program which is based on swab tests taken by nearly 100,000 people in England between June and July of 2021 and led by investigators from Imperial College.

“These findings confirm our previous data showing that both doses of a vaccine offer good protection against getting infected,” Paul Elliott, director of the REACT study said. “However we can also see that there is still a risk of infection, as no vaccine is 100% effective, and we know that some double vaccinated people can still become ill from the virus.”

For the study, the team of investigators analyzed prevalence trends and their drivers using reverse transcription-polymerase chain reaction (RT-PCR) swab-positivity data from the latest round of the REACT study, with swabs sent to non-overlapping random samples of the population ages 5 years and over in England.

The latest round of the study included 98,233 participants who swabbed themselves at home and had their samples analyzed by PCR testing.

Findings showed that of the participants, 527 were positive and 254 were successfully analyzed in a lab, showing 100% of them to be the delta variant. Of the participants who were unvaccinated, it was found that they had a 3 times higher prevalence than those who had received 2 doses of a vaccine.

The investigators determined that vaccinated individuals had between a 50% to 60% reduced risk of infection compared to those who were unvaccinated based on the data.

Additionally, those who received 2 doses of a vaccine were also less likely to test positive after coming into contact with someone who was infected with the disease.

“The Delta variant is known to be highly infectious, and as a result we can see from our data and others’ that breakthrough infections are happening in fully vaccinated people.” Steven Riley, professor of infectious disease dynamics at Imperial said. “We need to better understand how infectious fully vaccinated people who become infected are, as this will help to better predict the situation in the coming months, and our findings are contributing to a more comprehensive picture of this."