The Delta variant of the coronavirus can easily be transmitted from vaccinated people to their contacts in their homes, a British study by Imperial College London found on Thursday, although contacts are less likely to become infected if they are also vaccinated, according to Reuters.
The researchers pointed out that the results do not weaken the argument for vaccination as the best way to reduce the serious forms caused by COVID-19 and said that “booster” doses are needed to increase immunity.
The study found that infections in those vaccinated were shorter-lived, but the viral load at the peak of the infection remained similar to that of those unvaccinated.
“By conducting repeated and frequent sampling from contacts with COVID-19 cases, we found that vaccinated people can contract and transmit the infection to households, including vaccinated members,” said Dr. Anika Singanayagam, co-author of the study.
The researchers point out that the study now presents the reasons why the number of daily infections remains high even in some states with high vaccination coverage.
The study, which enrolled 621 participants, found that out of 205 contacts in the homes of people infected with the Delta variant, 38% of household contacts that were unvaccinated tested positive, compared to 25% of the vaccinated contacts.
Vaccinated contacts who tested positive for Covid-19 on average received their vaccines a long time ago than those who tested negative, which the authors said was evidence of a decrease in immunity and supports the need for booster vaccines.
Epidemiologist Neil Ferguson said the Delta’s transmissibility means that britain is unlikely to reach “herd immunity” for a long time.
“That can happen in the next few weeks: if the current transmission of the epidemic reaches peaks and then it starts to decline, by definition, in a way, we have reached herd immunity, but it will not be a permanent thing,” he told reporters.
“Immunity decreases over time, it is imperfect, so transmission takes place and that is why the booster program is so important,” the epidemiologist concluded.