The Delta variant of the coronavirus is of serious concern as laboratory tests have shown it to be more contagious and resistant to vaccines than other forms of COVID-19.
However, there is some evidence that the available jabs retain significant efficacy against it after two doses.
Here’s what you need to know:
A British study published in the medical journal The Lancet in early June looked at the levels of neutralizing antibodies produced in vaccinated people exposed to the Delta, Alpha (first identified in Britain) and Beta (first identified) variants. in South Africa).
It found that antibody levels in people who received two doses of the Pfizer-BioNTech vaccine were 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.
The Alpha and Beta variants also elicited weaker responses, with 2.6 times less antibody for Alpha and 4.9 times less for Beta.
A French study by the Institut Pasteur concluded that the neutralizing antibodies produced by vaccination with the Pfizer-BioNTech vaccine are three to six times less effective against the Delta variant than against the Alpha variant.
So, do vaccines still work?
Although they represent an essential marker, antibody levels measured in the laboratory are not sufficient to determine the effectiveness 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 effectiveness – and early results are reassuring.
According to data released Monday by Public Health England, vaccination with the Pfizer-BioNTech and AstraZeneca vaccines is as effective in preventing hospitalization in the case of the Delta variant as it is in the case of the Alpha variant.
Two doses of the Pfizer-BioNTech vaccine prevent 96 percent of hospitalizations due to the Delta variant, while the AstraZeneca vaccine prevents 92 percent, according to a study of 14,000 people.
Previous data released by British health authorities at the end of May lead to similar conclusions for milder forms of the disease.
The Pfizer-BioNTech vaccine is 88 percent effective against symptomatic COVID-19 caused by the Delta variant two weeks after the second dose, while the vaccine is 93 percent effective for cases caused by the Alpha variant.
AstraZeneca shows 60% effectiveness against cases caused by the Delta variant and 66% in the case of Alpha.
Scottish authorities published similar data in The Lancet on Monday.
Meanwhile, the team behind the Sputnik V jab tweeted on Tuesday that their vaccine was “more effective against the Delta variant … than any other vaccine that has published results on this strain so far.” They did not publish any results, but said the study by the Gamaleya Center, a Russian research institute, had been submitted for publication in an international peer-reviewed journal.
Is one stroke enough?
Of the vaccines available, only the Johnson & Johnson offering requires one dose – rather than two – to achieve efficacy. So far, there isn’t enough data to determine how it works compared to the Delta variant.
As for other jabs, lab and real-world tests conclude that one dose of any vaccine provides only limited protection against the Delta variant.
“After a single dose of Pfizer-BioNTech, 79% of people had a quantifiable neutralizing antibody response against the original strain, but that fell to… 32% for B.1.617.2 [Delta]”said the June lab study.
The Institut Pasteur found that a single dose of AstraZeneca would have “little or no effectiveness” against the Delta variant.
UK government data confirms the trend in real-world scenarios: Both vaccines were 33 percent effective against symptomatic cases caused by Delta three weeks after the first dose, compared to around 50 percent effective against the Alpha variant. .
In the UK – where the Delta variant is now responsible for 96% of new cases – the findings prompted the government on Monday to reduce the waiting period between doses from 12 weeks to eight for people over 40. .
In France, the wait has been reduced to three weeks against five for a second dose of Pfizer-BioNTech and Moderna vaccines.
However, the Pfizer-BioNTech jab offers very high protection (94%) against hospitalization due to the Delta variant after a dose.
So what is the best strategy against the Delta strain?
Scientists agree that the best defense against the Delta variant is to get a full vaccination in two doses.
French scientist Jean-François Delfraissy says creating a “block of vaccinated people” will help prevent the Delta variant from spreading throughout the population.
An American study from June 10 highlights the importance of vaccination to prevent the list of variants from growing.
“Increasing the proportion of the population immunized with current safe and effective licensed vaccines remains a key strategy to minimize the emergence of new variants and end the COVID-19 pandemic,” he said.
Antoine Flahault, who heads the Institute for Global Health at the University of Geneva, insists that it is always crucial to respect social distancing, share information about infections and observe restrictions if necessary to “Keep the virus circulating at a low level”.
The more the virus circulates, he says, the more opportunity it has to mutate and generate new variations.