The Delta variant of the coronavirus, first identified in India, is of global concern with studies showing that it is more contagious and resistant to vaccines than other forms of COVID.
But there is also evidence that vaccines maintain significant effectiveness against Delta after two doses.
This is what we know about how variants respond to blows.
Less antibodies …
Several laboratory tests show that the Delta variant appears to have stronger resistance to vaccines than the other variants.
A British study published in the medical journal The Lancet in early June examined the levels of neutralizing antibodies produced in vaccinated people exposed to the Delta, Alpha (first identified in Britain) and Beta (first identified in the UK) variants. South Africa).
Antibody levels were found in people with two doses of the Pfizer / BioNTech trait to be six times lower in the presence of the Delta variant than in the presence of the original COVID-19 strain on which the vaccine was based.
Alpha and Beta variants also elicited lower responses, with 2.6 times fewer antibodies for Alpha and 4.9 times less for Beta.
A French study by the Institut Pasteur concluded that neutralizing antibodies produced by vaccination with the Pfizer / BioNTech jab are three to six times less effective against the Delta variant than against the Alpha variant.
… but the vaccines still work
Although they represent an essential marker, the levels of antibodies measured in a laboratory are not sufficient to determine the efficacy of a vaccine.
In particular, they do not take into account a second immune response in the form of killer T cells, which attack already infected cells and not the virus itself.
As a result, real-world observations are crucial in measuring vaccine efficacy, and the first results are reassuring.
According to data released Monday by Public Health England, vaccination with Pfizer / BioNTech and AstraZeneca is as effective in preventing hospitalization in the case of the Delta variant as in the case of the Alpha variant.
Two doses of the Pfizer / BioNTech outbreak prevent 96 percent of hospitalizations due to the Delta variant, while AstraZeneca prevents 92 percent, according to a study involving 14,000 people.
Earlier data released by British health authorities in late May reach similar conclusions for less severe forms of the disease.
The Pfizer / BioNTech vaccine is 88% effective against symptomatic COVID caused by the Delta variant two weeks after the second dose, while the sting is 93% effective for cases caused by the Alpha variant.
AstraZeneca shows an efficiency of 60% against cases caused by the Delta variant and 66% in the case of Alpha.
Scottish authorities released similar data on Monday a The Lancet.
Meanwhile, the team behind Sputnik V tweeted on Tuesday that theirs is “more efficient against the Delta variant … than any other vaccine that has published results on this strain so far.”
They did not publish results, but said the study by the Gamaleya Center, a Russian research institute, had been submitted for publication in a peer-reviewed international journal.
Among the authorized vaccines, only one (developed by Janssen) is given in a dose instead of two, and there are not enough data to determine its effectiveness against the Delta variant.
For others, laboratory and real-world tests conclude that a dose of any vaccine it only provides limited protection against the Delta variant.
“After a single dose of Pfizer-BioNTech, 79% of people had a quantifiable response of neutralizing antibodies against the original strain, but this fell to … 32% for B.1.617.2 (Delta ), ”says the June lab study.
The Pasteur Institute found that a single dose of AstraZeneca would have “little or no efficacy” against the Delta variant.
British government data confirm the trend in real-world scenarios: both vaccines were 33% effective against symptomatic cases caused by Delta 3 weeks after the first dose compared to 50% effectiveness against the Alpha variant.
In the UK, where the Delta variant is now responsible for 96 per cent of new cases, these findings pushed the government on Monday to reduce the waiting period from doses of 12 weeks to eight for people over 40.
In France, the wait has been reduced from five to three weeks for a second dose of Pfizer / BioNTech and Moderna vaccines.
The Pfizer / BioNTech outbreak, however, offers very high protection (94%) against hospitalization due to the Delta variant after a dose.
Shots and social distancing
Scientists agree that the best defense against the Delta variant is to get a full two-dose coronavirus vaccine.
Top French scientist Jean-François Delfraissy says creating a “block of vaccinated people” will help prevent the Delta variant from spreading throughout the population.
A US study on June 10 points to the importance of vaccination to keep the list of variants growing.
“Increasing the proportion of the immunized population with current safe and effective authorized vaccines remains a key strategy to minimize the emergence of new variants and end the COVID-19 pandemic,” he says.
Antoine Flahault, who heads the University of Geneva’s Institute for Global Health, insists it is still crucial to observe social distancing, share information about the infection, and observe restrictions when necessary to “keep the virus circulating low.”
The more the virus circulates, he says, the more opportunities it has to mutate and generate new variations.
© 2021 AFP
Citation: COVID-19: How do vaccines against the Delta variant (2021, June 16) recovered on June 16, 2021 at https://medicalxpress.com/news/2021-06-covid-vaccines-delta-variant. html
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