1 What is the difference with the vaccines administered so far?
The RNA vaccines from Pfizer-BioNTech and Moderna are, by far, the most administered in France since the start of the covid-19 pandemic. They were designed based on the original Wuhan virus which has since been replaced by other variants.
With the arrival of the very singular Omicron, at the end of 2021, the two competitors decided to update the formulation of their product, by offering bivalent vaccines, that is to say which contain half of the RNA of the Wuhan strain, and for the other half of Omicron’s RNA.
Pfizer and Moderna started by integrating that of the “first version” of Omicron, the BA.1 sub-lineage. But, since June, it is the BA.4 and BA.5 sub-lineages that are responsible for most of the contaminations in the world. So Pfizer and Moderna decided to produce another type of bivalent vaccine mixing RNA? of these two sub-variants to that of the Wuhan strain.
2 Why produce vaccines based on newer strains?
“These bivalent vaccines will be used to update our immune system so that it can better recognize these new variants”, explains Sandrine Sarrazin, researcher at the Marseille-Luminy immunology center (CNRS/Inserm/Aix-Marseille University).
“They will allow the production of antibodies better suited to neutralize the virus fairly quickly, but also to update another line of defense, that made up of memory B and T cells, which protect us against serious forms”, completes- she.
3 Is their effectiveness more important?
Bivalent vaccines mixing Omicron’s Wuhan and BA.1 strains have been tested in clinical trials – on human subjects – by Moderna and Pfizer. Administered as a second booster dose, they produced a better neutralizing antibody response against BA.1 than that induced by the first generation of vaccine.
Big downside: these bivalent vaccines, based on BA.1, generated a response? against the BA.4 and BA.5 sub-variants, certainly good, but between three and five times weaker than against BA.1.
Launched more recently, the bivalent vaccines based on the strains of Wuhan and BA.4/BA.5 are also the subject of clinical studies. But their results are not yet known. Data obtained from animal models have nevertheless shown promise in terms of immune response.
If confirmed, will these good results be synonymous with enhanced efficacy against the transmission of the virus, a weak point of current vaccines? “We will have information when we have started injecting these new bivalent vaccines into the population. But in theory, yes. At the start of the pandemic, we benefited from good efficacy against the transmission of the virus when the vaccines were well adapted to the circulating strain of Wuhan, ”answers Sandrine Sarrazin.
4 Are they safe?
The American and European health authorities have indicated that the side effects observed with the bivalent vaccines were “comparable” to those observed with the original vaccines.
“Now that it has been demonstrated that RNA anti-covid vaccines are safe and effective, it is considered that the few RNA modifications made for bivalent vaccines will not change their overall functioning”, assures Sandrine Sarrazin.
5 What about authorization requests?
In the United States, the Food and Drug Administration (FDA) issued authorizations for Moderna and Pfizer’s BA.4/BA.5-based vaccines on August 31. She had urged, as early as June, to benefit from bivalent vaccines based on these two strains.
In Europe, the European Medicines Agency (EMA) is following suit. First, it validated the bivalent BA.1 vaccines from the two laboratories on September 1. And this Monday, it authorized that of Pfizer based on BA.4 / BA.5 which can be used as a booster dose, for those over 12 years old who have already been vaccinated.
While clinical data is lacking for this latest vaccine, the EMA says it has made its decision, in particular based on the information available for the bivalent BA.1 vaccine, which is “closely related” to it. It also specifies that it “will receive new clinical data as it is generated”.
A green light without a clinical trial, isn’t that worrying? “This strategy of authorizing a vaccine only on preclinical data in animals is the one used for the flu every year”, recalls Sandrine Sarrazin.
6 Who can benefit and when?
To be authorized in France, these bivalent vaccines must receive a favorable opinion from the High Authority for Health. She plans to make her decision “mid-September”.
Pfizer has already announced that doses “will be able to be shipped shortly after obtaining the respective regulatory approvals and can be used as early as September”.
While an epidemic resumption is observed in the country, these adapted vaccines should be integrated into the fall vaccination campaigns. The EMA recommends that “these reminders should be given in priority to people who are at greater risk of serious illness due to certain risk factors”.
The immunologist Sandrine Sarrazin, however, warns fragile people whose last booster dose is starting to date: “Current vaccines remain very effective against serious forms, it is better to receive a fourth dose now than to take the risk of waiting , a month, the arrival of a bivalent vaccine”.
letelegramme Fr Trans