COVID-19: The effectiveness of vaccines on the delta variant is in question

COVID-19: The effectiveness of vaccines on the delta variant is in question

Several laboratory studies suggest that the delta variant (formerly called the “Indian version”) appears to be more resistant to vaccines than other variants (this is referred to as “immune escape”). One of these studies was conducted by British authorities and published in the medical journal The Lancet in early June. Their findings: In people vaccinated with two doses of Pfizer/BioNTech, levels of neutralizing antibodies are about six times lower in the presence of the delta variant than in the presence of the historical strain of the virus (which has been used to develop vaccines). was done for) )

By comparison, this reduction is “only” 2.6 times compared to the alpha version (or “English version”), and 4.9 times compared to the beta version (“South African”). Another study conducted in France by the Institut Pasteur concluded that neutralizing antibodies produced by vaccination with Pfizer/BioNTech are three to six times less effective against the delta version than with the alpha version. Although this is an essential indication, antibody levels measured in the laboratory are not sufficient to determine the effectiveness of a vaccine.

Indeed, it does not take into account the second part of the immune response, cellular immunity (due to cells called lymphocytes). Hence the importance of seeing what is happening in real life. And the first results in the real population are reassuring.

According to data released by British authorities on Monday, vaccination with Pfizer/BioNTech and AstraZeneca is as effective in preventing hospitalization in the delta version as in the alpha version. According to this study involving 14,000 people, the two doses prevented 96% (for Pfizer/BioNtech) and 92% (for AstraZeneca) from hospitalization due to the delta variant. Previous official English data communicated at the end of May reached comparable conclusions for less severe forms of the disease.

Two weeks after the second dose, the Pfizer/BioNTech vaccine is 88% effective against the symptomatic form of COVID caused by the delta variant, compared to 93% for the alpha variant. AstraZeneca, for its part, shows a performance of 60% and 66% over these variants. Similar data was published by Scottish authorities in The Lancet on Monday.

Finally, the designers of the Russian vaccine Sputnik V assured on Twitter on Tuesday that it was “more effective against the delta variant” than any other vaccine at this stage. However, he did not publish his data, according to him sent to a medical journal.

one dose is not enough

In the laboratory or in real life, studies converge on one point: receiving a single dose of the vaccine provides only limited protection against the delta variant. “After a single dose of Pfizer/BioNTech, 79% of people had a detectable antibody response against the original strain (of the virus), but this was 50% for the alpha variant, 32% for the delta variant, and 25% for the variant beta,” concludes a laboratory study published in early June in The Lancet.

According to the Pasteur Institute, a single dose of AstraZeneca will be “small or not effective at all” against the delta variant. Trends confirmed in real life: According to British officials, a single dose of either of the two vaccines is only 33% effective in preventing the symptomatic form of the disease caused by the delta variant (and 50% for the alpha version). )

On the other hand, when it comes to avoiding hospitalization due to the delta variant, the first dose of Pfizer/BioNTech already provides very high protection (94%). Of all the authorized vaccines, only a single dose of Janssen can be attributed. However, specific data on its effectiveness against the delta variant are not available.

Faced with the risk that people will be inadequately protected against the delta variant if their vaccinations are not completed, the British government on Monday decided to shorten the interval between doses. For those over 40, it goes up to 12 to 8 weeks. In France, this gap can now be reduced to 3 weeks (compared to a minimum of 5 weeks earlier) for vaccines from Pfizer/BioNTech and Moderna.

And later ?

To protect against the emergence of the delta variant, which according to British officials is 60% more permeable than alpha, scientists emphasize the importance of complete vaccination with both doses. To create this “block of vaccinated individuals”, according to the image of Jean-Fran├žois Delfraissy, president of the French Scientific Council, has a second purpose: to prevent the emergence of other forms among populations that are only partially, Or not at all, protected.

Because beyond the alpha version, the possibility that worries scientists is the appearance of future variants that are more resistant to vaccines. A US study published on June 10 in the journal Nature outlines, “Increasing the proportion of the immunized population with current vaccines that are safe and effective is an important strategy to reduce the emergence of new forms and end the Covid pandemic.” is.”

However, “we don’t have to base everything on vaccinations,” epidemiologist Antoine Flehault told AFP. He considers it important to “keep the circulation of the virus very low” through all other containment measures (barrier gestures, identification of cases to break the chain of transmission, restrictive measures where necessary…). Because the more the virus spreads, the more it has the opportunity to mutate and therefore give rise to other forms.

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