COVID-19: vaccines protect against delta variant, but do not stop domestic transmission

Preparations against COVID-19 reduce the risk of infection from the delta variant, but those immunized with the full regimen can still transmit the virus to vaccinated and unvaccinated cohabitants, reveals a study published in “The Lancet.”

This is demonstrated by an analysis carried out between September 2020 and 2021 in the United Kingdom with 621 participants identified through the British screening system as positive with mild disease or asymptomatic.

Likewise, the authors recorded demographic and vaccination information of those enrolled, while performing daily PCR tests to detect COVID-19, regardless of whether they had symptoms or not.

It is, the researchers note, one of the few studies developed so far that includes such a large amount of detailed household data, which offers key information to know how those vaccinated with delta can still become infected and transmit this variant.

In this context, the experts identified a total of 205 domestic contacts of cases of the delta variant, of which 53 tested positive for COVID-19.

Of these 205 contacts, 62% (126) received two doses of a vaccine, 19% (39) had received one dose of a preparation, and another 19% (40) were not vaccinated.

Among household contacts who were immunized with the full schedule, 25% (31 of 126) were infected with the delta variant, compared with 38% (15 of 40) of unvaccinated household contacts.

“Vaccines are key to controlling the epidemic, as we know they are very effective in preventing serious illness and deaths from COVID-19. However, our results show that vaccination alone is not enough to prevent others from becoming infected with the delta variant and to prevent it from spreading in the domestic setting.“, Explain Ajit Lalvani, from Imperial College London and co-author of the study.

They also found, contributes, that the “susceptibility to infection“Had already increased a few months after the second dose of the vaccine,”so those eligible for booster injections should receive them immediately”.

The authors insist that, unlike the unvaccinated, those vaccinated with the complete regimen present a lower risk – although still appreciable – of being infected with the delta variant, while “clear the infection more quickly”.

However, the peak of viral load among the vaccinated is similar to that of the unvaccinated, which could explain, they add, why those can still transmit the virus easily within the home.