COVID-19 Delta variant

People who are fully vaccinated with a two-dose coronavirus vaccine have a 50% to 60% reduced risk of being infected with the delta variant.

The study examined nearly 100,000 people who took COVID-19 swab tests at home 527 patients tested positive for the coronavirus in that sample set, and 254 of the samples were genetically investigated; all of the sequenced samples were found to be the highly transmissible delta variant.

After accounting for characteristics such as age, the researchers discovered that those who received two vaccine doses were 49 percent more likely to test positive for the coronavirus even if they had no symptoms, and that vaccinated people were 59 percent less likely to test positive with symptoms.

Meanwhile, early data from Israel suggested that the Pfizer-BioNTech vaccine was 64% effective against symptomatic disease caused by the delta variant, and data from Canada found it was 87% effective against symptomatic disease

Newer data from Israel found that the efficacy of the Pfizer-BioNTech vaccine against Delta slipped to 39% (but is still 88% effective against hospitalization and 91% protective against severe illness.

Vaccinated people also had a lower viral load on average, implying that they shed less virus and are less contagious than unvaccinated people, according to the current study. Other research has suggested that the delta variation causes equivalent virus levels in unvaccinated and vaccinated patients who test positive.

“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, a professor of infectious disease dynamics at Imperial College London, said in the statement. “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.”

The infection rate was highest among young people aged 13 to 24, and lowest among those aged 75 and up. Riley told Reuters that people aged 5 to 24 accounted for over half of the infections, but accounting for barely a quarter of the population.

“Today’s report shows the importance of taking personal responsibility by self-isolating if you are contact traced, getting tested if you have symptoms and wearing face coverings where appropriate,” U.K. Health and Social Care Secretary Sajid Javid said in the statement. “I urge anyone who has yet to receive a vaccine to get jabbed and take up both doses — the vaccines are safe, and they are working.”

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