It spread like wildfire. After its appearance and rapid diffusion in India, a few weeks were enough for the Delta variant to spread across the globe and replace the Alpha variant. A more contagious Delta variant, which causes immune escape. According to a study conducted by researchers at the prestigious Mayo Clinic in the United States, and pre-published on the platform
MedRxiv, the messenger RNA (mRNA) vaccine from Pfizer would be less effective against this strain than that of Moderna, but would nevertheless confer significant protection against the risks of severe forms of the virus and hospitalization.
So how effective are messenger RNA vaccines against the Delta variant? 20 minutes make the point.
Only 42% effective against the Delta variant?
To conduct their study, the American researchers analyzed real-life data on a sample of nearly 50,000 people: one half vaccinated and the other not, and compared the effectiveness of the two mRNA vaccines on the Alpha and Delta variants. . Data collected between January and July 2021, a period covering the epidemic wave of variant Alpha at the beginning of the year, and that caused by the variant Delta since the beginning of summer.
The researchers found that the two vaccines effectively protected against an Alpha variant infection, at 86% for Moderna and 76% for Pfizer, and from hospitalization linked to Covid-19, at 91.6% for Moderna and at 85% for Pfizer. But “in July [mois durant lequel le variant Delta représentait 70 % des contaminations] the efficacy against infection was markedly lower with the Moderna vaccine and with that of Pfizer, with an even more pronounced drop for the latter, ”the researchers noted. They observed that the efficacy of the two sera against the transmission of the Delta variant decreased to 76% for the Moderna vaccine, and fell to only 42% for that of Pfizer. “If that’s not a red flag, I don’t know what it is,” a senior Biden administration official told the media. Axios.
At this time, it is not known whether these results mean a decrease in vaccine effectiveness over time, a decrease in effectiveness against the Delta variant, or a combination of the two. “Based on the data we have so far, this is a combination of the two factors. The Moderna vaccine is most likely more effective than the Pfizer vaccine in areas where Delta is the dominant strain, and the Pfizer vaccine appears to have lower durability of effectiveness, ”study co-author Venky Soundararajan told Axios . But “we know that the quantity of neutralizing antibodies tends to decrease in the months following vaccination. However, our team has shown, like other teams, that it takes about four times more antibodies to neutralize the Delta than it takes to neutralize the Alpha ”, explained to the World Prof. Olivier Schwartz, virologist at the Institut Pasteur, who conducted a study
published in the journal Nature.
Favor Moderna? “For now, this is only a hypothesis”
For the French health authorities, this study alone does not justify reviewing the vaccine strategy deployed so far. “This is a preprint [pas encore validé par la communauté scientifique], a unique study, the content of which is not the subject of a scientific consensus, replies the Ministry of Health to 20 minutes. Is the Moderna vaccine really more effective or – since it is less used than Pfizer – has the virus been able to adapt due to the vaccination coverage of the population? It is early to learn lessons from the vaccine orders ”placed by France.
“This study is in prepublication” and “has not benefited from a peer review”, also estimated on CBS Dr.Anthony Fauci, Covid advisor to US President Joe Biden. A study which will be the subject of further work. In the meantime, France is ready to focus on the serum developed by Moderna. “From the end of August, we will go from 600,000 weekly doses of Moderna to 2 million, with a vaccine mix that will rebalance in favor of Moderna,” the ministry assures us. We are therefore able to favor – if necessary – the Moderna vaccine. But for the moment, this is only a simple hypothesis ”.
Increase immunization coverage
Especially since if it was confirmed that mRNA vaccines lose their effectiveness against the transmission of the Delta variant, researchers at the Mayo Clinic have nevertheless observed “their effectiveness against the risks of hospitalization remains high: 81% for Moderna and 75% for Pfizer ”. While 40 million French people are fully vaccinated, for the government, there is no question of slowing down the pace: the vaccination coverage in France must increase further, and quickly, especially in the West Indies and Polynesia, where the low vaccination coverage coincides with the virulence of the fourth wave. To “limit the rapid spread of the Delta variant on the territory, vaccination constitutes the most effective weapon to prevent hospitalizations and death, insists the High Authority of Health (HAS) in one of its latest opinions. The efficacy of mRNA vaccines on the prevention of severe forms of Covid-19 has been established, including against the Delta variant ”. And the more the population is vaccinated, the more the reservoirs of circulation of the virus decrease, and with them the risks of seeing new more virulent variants appear.
For its part, the Pfizer – BioNTech duo said in a press release “hope to be able to develop and produce a tailor-made vaccine against this variant [Delta] within about 100 days of the decision being made, and submit it to regulatory authorities ”. And it would be in his interest to work on this formula. A British study published on Thursday reveals that while it is more effective in fighting infections linked to the Delta variant of the coronavirus, the Pfizer vaccine loses its effectiveness more quickly than that of AstraZeneca.