COVID-19

Covid-19: two doses of vaccine minimum to protect against variants

Efficacy has undoubtedly been diminished, but protection against Covid-19, provided both doses are received, is still very important: an update on what we know about the effects of vaccines against the Delta variant, which is causing concern across the planet.

Reduced efficiency …

Several laboratory studies show that the Delta variant (formerly called the “Indian variant”) appears to be more resistant to vaccines than the other variants (this is called “immune escape”).

One of these studies was conducted by the British authorities and published in early June in the medical journal The Lancet. His findings: in people vaccinated with two doses of Pfizer / BioNTech, neutralizing antibodies are almost six times lower in the presence of the Delta variant than in the presence of the historical strain of the virus. (which was used to develop vaccines).

For comparison, this is a reduction of “only” 2.6 times compared to the Alpha (or “English” version) and 4.9 times compared to the Beta (“South African”) version.

Another study by the Institut Pasteur in France concluded that the neutralizing antibodies produced by Pfizer / BioNTech vaccinations are three to six times less effective against the Delta variant than against the Alpha variant.

… but still effective

While this is an important metric, antibody levels measured in a laboratory are not sufficient to determine whether a vaccine is effective. Indeed, this does not take into account the other part of the immune response, cellular immunity (associated with cells called lymphocytes).

Hence, it is important to look at what is happening in real life. And the first results in the real population are encouraging.

According to figures released on Monday by the British authorities, vaccination with Pfizer / BioNTech and AstraZeneca is as effective in preventing hospitalizations with Delta as with Alpha.

Two doses prevented 96% (for Pfizer / BioNTech) and 92% (for AstraZeneca) hospitalizations due to the Delta variant, according to this 14,000-person study.

Previous official data in English, presented at the end of May, allowed comparable conclusions to be drawn 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, versus 93% when it comes to the Alpha variant. For its part, AstraZeneca demonstrates 60% and 66% efficiency compared to these options.

Similar figures were published by the Scottish authorities on Monday in The Lancet.

Finally, the developers of the Russian Sputnik V vaccine reassured on Twitter on Tuesday that it is “more effective against the Delta variant” at this stage than any other vaccine. However, they did not publish their data, which they said was sent to a medical journal.

One dose is not enough

In the laboratory or in real life, research converges on one thing: receiving a single dose of 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 parental strain (virus), but this response dropped to 50% for the Alpha, 32% for the Delta and 25% for the Beta,” the laboratory concludes. study published in early June in The Lancet.

According to the Pasteur Institute, a single dose of AstraZeneca will be “ineffective or not effective at all” against the Delta variant.

The trends are confirmed in real life: according to the British authorities, 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% when it comes to the Alpha variant.).

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 approved vaccines, only the Janssen vaccine can be attributed to a single dose. However, there is no specific data on its effectiveness against the Delta variant.

Faced with the risk that people will not be adequately protected from the Delta variant if their vaccinations are not completed, the British government decided on Monday to reduce the interval between doses. For those over 40 – 12 to 8 weeks.

In France, this gap can now be reduced to 3 weeks (up from a minimum of 5 weeks previously) for vaccines from Pfizer / BioNTech and Moderna.

And after ?

To protect against the emergence of the Delta variant, which the British authorities claim is 60% more infectious than Alpha, scientists emphasize the importance of full vaccination with both doses.

The formation of this “block of vaccinated persons”, in the image of the president of the French Scientific Council, Jean-François Delfrassy, ​​has a second goal: to prevent the emergence of other variants among populations that are only partially, if at all, protected.

Because outside of the alpha option, scientists are worried about the prospect of future options that will be much more resistant to vaccines.

“Increasing the proportion of the population immunized with modern vaccines that are safe and effective is a key strategy for minimizing the emergence of new variants and ending the Covid pandemic,” underlines the American study published June 10 in the journal Nature.

However, “we should not base everything on vaccination,” epidemiologist Antoine Flaho told AFP.

He considers it essential to “maintain very low circulation of the virus” through all other control measures (barrier gestures, case finding to break the chain of transmission, restrictive measures where necessary, etc.). Since the more the virus circulates, the more opportunities it has to mutate and, therefore, give rise to other variants.


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