Coronavirus, only two doses of the vaccine protect against the Delta variant

“A single dose of Pfizer or AstraZeneca vaccine is not enough to protect against the new Delta variant, while the two doses of both vaccines are able to block it, even if slightly less than the other vaccines” is what a recent study reveals. of the French Pasteur Institute published in Nature.

The Delta variant was first detected in India last October. It is already present in 98 countries. It is thought to be 60% more contagious than the Alpha variant, initially detected in the UK.

Delta has several mutations that could make antibodies generated by people who have had COVID or by those who are vaccinated not as effective.

The French study was carried out in the laboratory and was based on measuring the effectiveness against the virus of antibodies, the proteins of the immune system capable of blocking the pathogen’s entry into cells.

The team analyzed whether antibodies from people who have had COVID and those from those who received one or two doses of the vaccines neutralize the Delta variant. They also analyzed the neutralizing ability of Bamlanivimab, an antibody-based drug manufactured by Eli Lilly. The study involved 162 patients, 59 of whom received one or two doses of the vaccine.

The results showed that the antibodies of people who have overcome Covid are not very effective against the Delta. But this effectiveness increases by several orders of magnitude when it comes to people who have had the disease and have also received a dose of the vaccine. It is a similar scenario to that seen with uninfected people receiving the vaccine. Antibodies generated with a single dose of Pfizer or Astrazeneca cannot stop the virus in laboratory culture dishes, but they do when the full regimen is in place. Field trials have confirmed these data. An official UK study of over 14,000 infected with the Delta variant showed Pfizer / BioNTech and Astrazeneca vaccines prevented over 90% of hospitalizations. Of course, a single dose of the vaccine is 17% less effective against the new variant than the rest.

Despite these good results Pfizer and BioNTech have announced that they have already produced a new version of their drug to combat the Delta variant.

The companies will begin clinical trials in August. Both companies are also promoting a third booster dose. A third vaccination would increase the levels of antibodies against the delta variant five to tenfold.

Pfizer’s data is in contrast to that provided by Moderna, the manufacturer of the other messenger RNA-based vaccine. Ten days ago, the company announced that it observed only a “moderate” decrease in the level of antibodies generated by the Delta variant vaccine. “These new data are encouraging and reinforce our confidence that the vaccine should continue to protect against new variants detected,” explained Stéphane Bancel, Moderna CEO.


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