Covid-19 vaccines protect against severe forms of this disease, but are not as effective at preventing infections and transmission since the Delta variant is in the majority. An English study looked at contaminations and the dynamics of contaminations within the home, where the coronavirus is most easily transmitted.
It is at home, where barrier gestures and masks fall, that SARS-CoV-2 spreads most easily.is an effective bulwark to reduce the risk of being contaminated, but far from being infallible, especially against the Delta variant. , conducted atImperial College of London, concludes that a complete vaccination schedule confers very partial protection – but still greater than in the absence of vaccination – against the Delta variant in the context of domestic transmission.
« Our results show that vaccination alone is not sufficient to prevent people from becoming infected with the Delta variant, and spreading it beyond, into homes. This is probably the case for other enclosed places where people spend long periods of time nearby. This will happen more and more as we head into winter »,, professor at National Heart & Lung Institute to theImperial College of London and who co-directed this study.
Transmission still possible despite vaccination
Between September 2020 and September 2021, scientists followed 621 participants identified by the contact tracing set up in the UK. The participants in this study, generally young and in good health, reported only mild or asymptomatic forms of the disease.. Among them, 163 were tested positive for SARS-CoV-2: 71 by the Delta variant, 42 by the Alpha variant and 50 by the original variant. Among the 71 people infected with , 23 are unvaccinated, 10 partially vaccinated and 54 fully vaccinated. These 71 people are , that is to say that they are considered as the starting point of a chain of contamination. Scientists have regularly monitored and tested the people with whom the index cases have been in contact in their homes; these are the contact cases. In total, the 71 index cases attended 205 contact cases, of which 53 caught the .
Among the 205 contact cases, 126 have a complete vaccination schedule, 39 are partially vaccinated and 40 are unvaccinated. The scientists then crossed the vaccination status of the contact cases tested positive for the Delta variant: 25% of them were fully vaccinated and 38% unvaccinated. While vaccination decreases the risk of being infected with the Delta variant, the probability of being infected remains significant. Using this data, scientists from theImperial College of London estimated thatare 34% effective in preventing infection with the Delta variant.
The peak of the viral cycle
In addition to monitoring contamination within homes, scientists also monitored thein 133 patients, vaccinated or not. Every day, the amount of coronavirus in their body was estimated by PCR. Scientists observed that the viral peak, when the number of is higher, is of the same magnitude in vaccinated and unvaccinated. British scientists believe that it is because of this very intense peak that the Delta variant manages to be transmitted so easily, even in vaccinated people. In contrast, the viral load decreases more quickly in people who have been vaccinated.
The work of scientists fromImperial College of London underlines an important fact: vaccination alone, especially against the Delta variant and at the beginning of thecold is not sufficient to stem the transmission of SARS-CoV-2. Airing confined spaces, social distancing, masks or hand washing are all reflexes that break the chains of transmission. In addition, vaccines remain terribly effective in fulfilling their primary function: .