Covid-19: faced with the Delta variant, the effectiveness and limits of RNA vaccines – archyde

Essential to limit the health damage from Covid-19, the vaccine will not be sufficient to stop, on its own, the circulation of the new coronavirus in the population. In particular, the reduced efficacy of the Pfizer-BioNTech vaccine – and to a lesser extent that of Moderna – against the Delta variant, now the majority in France.

In a pre-publication posted August 9 on the MedRxiv portal, researchers from the American university hospital network Mayo Clinic and the data analysis company Nference offer the first comparative and quantified estimate, in real life, of the efficiency of the two messenger RNA vaccines. These data suggest maintaining a high level of protection, greater than 75%, against severe forms of the disease, against Delta.

But protection against infection – symptomatic or not – falls ahead of the variant that appeared in India and drops to just over 40% for Pfizer. The Moderna, much less used in France, retains a high level of protection. The prospect of rapidly achieving group immunity through vaccination alone is thus fading even further.

Call for further studies

These figures, not yet formally published, must be considered with caution. But, according to scientists contacted by The world, they are credible and above all consistent with other evidence already available. The authors analyzed hospitalization and RT-PCR test result data from Mayo Clinic, obtained in January and July, on more than 25,000 patients in Minnesota. They then retrospectively compared the health fate of unvaccinated people with those who received two doses, selecting those over 18 and taking into account gender, ethnicity and date of vaccination.

The researchers were thus able to assess the effectiveness of the two vaccines against the Alpha (known as “English”) and Delta (“Indian”) variants, by relying on the fact that in Minnesota the former was largely dominant in January and the second in July. The results speak for themselves. Facing the Alpha, Pfizer would offer 85% protection against hospitalization and 76% protection against infection, with Moderna providing 91.6% and 86% protection against these events, respectively. Against the Delta, Moderna only protects 81% against hospitalization and 76% against infection, while Pfizer retains a protection rate of 75% against hospitalization, but only 42% against the infection.

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