Will it be three doses rather than two? The Pfizer / BioNTech alliance will test the effectiveness of a third dose of its covid-19 vaccine on participants in the initial clinical trial. The objective: to assess the possible effect of this vaccine on immune strengthening, in particular against variants of the coronavirus, the two companies announced on February 25.

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“Wakeup call”

Pfizer and BioNTech thus wish to evaluate “safety and the way in which a booster injection is tolerated“. Concretely, all participants of phase 1 of their clinical trial in the United States will thus be offered a third dose”six to 12 months“after receiving the first two, themselves spaced 21 days apart.

This test fits “as part of the clinical development strategy of the two companies to assess the efficacy of a third dose against variants“in circulation, or future.

Be careful with variants

For now, the two companies want to be reassuring about the variants. They specify in fact that they have not observed any change in “antibody levels“after injection of their vaccine against the variants. Which means that there would be no”significant reduction in the protection provided“by the two classic doses against the new strains of virus.

The study conducted under real conditions in Israel on February 24 in the NEJM, at a time when the British variant was circulating in the country, is also reassuring and shows that the Pfizer vaccine is indeed effective against this variant.

But caution remains in order, especially in the face of the South African variant. Because the mutations it presents seem to allow it to counter the immune defenses developed after certain treatments such as vaccines.

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Third dose or modified vaccine?

This South African variant and those who present the same mutations could require laboratories to review their vaccine formulas. Pfizer and BioNTech have also indicated that they are in “discussions with regulatory authorities“to submit an amended version of their vaccine”with a sequence specific to the variants“.

And the process is already underway for biotech company Moderna, which announced on February 24 that a modified version of its vaccine, developed specifically against the South African variant, was ready to be tested on humans in trials. clinics.

No need for long clinical trials

That doesn’t mean, however, that manufacturers will have to start from scratch. On February 22, the United States Medicines Agency (FDA) indicated that laboratories would not have to conduct lengthy clinical trials for modified versions of their already authorized vaccines. Less extensive testing will be sufficient, which should greatly accelerate their time to market in the event of conclusive results.

This is already happening, for example, with modified versions of influenza vaccines every year.