Fully vaccinated adults can harbour virus levels as high as unvaccinated people if infected with the Delta variant, according to a sweeping analysis of UK data, which supports the idea that hitting the threshold for herd immunity is unlikely.
There is abundant evidence that Covid vaccines in the UK continue to offer significant protection against hospitalisations and death. But this new analysis shows that although being fully vaccinated means the risk of getting infected is lower, once infected by Delta a person can carry similar virus levels as unvaccinated people.
The implications of this on transmission remain unclear, the researchers have cautioned. “We don’t yet know how much transmission can happen from people who get Covid-19 after being vaccinated – for example, they may have high levels of virus for shorter periods of time,” said Sarah Walker, a professor of medical statistics and epidemiology at the University of Oxford.
“But the fact that they can have high levels of virus suggests that people who aren’t yet vaccinated may not be as protected from the Delta variant as we hoped.”