The effectiveness of the vaccine would decrease over time
Even if vaccines remain the best solution against the Covid-19 virus, studies question their effectiveness against the Delta variant.
The amount of virus found in infected vaccinated people is comparable to that of unvaccinated people. (Illustrative photo)
KEYSTONE/Cyril Zingaro
Recent data cast doubt on the level of effectiveness of vaccines in preventing Delta variant infection and transmission. Vaccines remain despite everything the best bulwark.
The vaccines remain extremely effective against severe forms of Covid-19 but offer only partial protection against infection with the Delta variant, now dominant in the world, British and Israeli figures show.
A large English study carried out from June 24 to July 12 and made public on Wednesday concluded that the vaccine was “imperfectly effective against infection”. The vaccine is 49% effective against infection in 18 to 64 year olds, a rate that rises to 59% for symptomatic infections.
Vaccinated people are three times less likely to test positive. “There is always a risk of infection, no vaccine is 100% effective,” said Paul Elliott, head of the study. Six weeks earlier, another British study concluded that the Pfizer / BioNTech vaccine was 88% effective against the symptomatic form of Covid-19 caused by the Delta variant, and AstraZeneca, 60%.
Reduced immunity
In Israel, confronted later with this variant, official data published on July 22 shows an effectiveness of only 39% of the Pfizer / BioNTech vaccine against contamination, and of 40.5% against a symptomatic Covid.
The figure of 39% should be taken with caution, warn several epidemiologists, however, because it related to a period when Israel recorded relatively few cases in total (between June 20 and July 17).
If confirmed, these declining efficacy rates could be a sign of a decline in immunity in those vaccinated for months, or of an increased ability of the Delta variant compared to previous strains to overcome defenses. immune, thanks in particular to its ability to replicate more quickly.
Contagious infected vaccines
The study of a cluster in the state of Massachusetts, unveiled last week, surprised by the amount of virus found in infected vaccinated people, comparable to that of unvaccinated.
“Some people infected with the Delta variant after vaccination can be contagious and transmit the virus to other people,” said Rochelle Walensky, director of the US Centers for Disease Prevention and Control (CDC), calling the data ” worrying ”. Here again, specialists urge caution.
Lower viral load
“So far, all the other studies have shown that infected vaccinated people have a lower viral load, and therefore probably transmit much less than do unvaccinated people”, explains to AFP the immunologist Claude- Agnès Reynaud, research director at CNRS.
“It is important to note that the (screening tests) RT-PCR measure the viral RNA” (the amount of genetic material of the virus) and “not the infectious virus”, also underlines the virologist Angela Rasmussen, on Twitter.
It is therefore “difficult to say on the basis of these data alone” that vaccinated people are also contagious, even if the precaution requires “to act as if they were,” said the researcher affiliated with Georgetown University.
Shorter time
In addition, “vaccinated people who are infected (…) excrete the virus for a shorter period of time, they will be contagious for a shorter period”, underlined the French infectious disease specialist Odile Launay, citing a Singaporean study on hospitalized patients.
These data confirm that the vaccine does not provide an “immunity totem” and that the coronavirus can continue to circulate in vaccinated people. But they should not forget the essential: the number of people infected by each new positive case will be much lower if it is in the presence of vaccinated people, more difficult to infect.
Vaccination “creates a barrier to the transmission of the virus at the population level”, summarizes Angela Rasmussen. “The problem is, there aren’t enough barriers” for the virus to “fail to find a new host” and stop circulating, she adds. This pleads for the maintenance of “additional barriers”.
“This is why today, we ask people to continue to wear the mask in closed environments, gatherings and near vulnerable people”, also emphasizes Odile Launay. This is the conclusion drawn by the US health authorities, who once again recommended wearing masks indoors for people vaccinated in high-risk areas.
Found an error? Report now.
–
