this is how new vaccines work

An adaptation to the evolution of viruses

The Covid-19 disease virus, Sars-CoV-2, has the capacity to mutate, like other viruses. It is a natural mechanism: viruses multiply and accidental genetic modifications can take place, depending on the replication of their DNA.

The first vaccines were developed from the initial strain, known as Wuhan. Since then, other variants have emerged, such as Delta or Omicron. The latter in fact represents a family of variants, of which several sub-lines are currently circulating, such as BA.1. Omicron and its sub-variants have been dominant throughout 2022, quickly taking the place of previous Alpha and Delta variants. Today, it is essentially Omicron’s BA.5 sub-variant that dominates in Europe and the United States.

It is to better respond to these mutations that pharmaceutical groups adapt their vaccines. A concept that is not new: in the case of vaccination against influenza, for example, quadrivalent vaccines – developed with components from two strains of the influenza A type and two influenza type B viruses – are used.

Bivalent vaccines

In the case of Covid, so-called bivalent vaccines are designed for the same purpose: to educate the immune system to recognize several attackers. The American-German tandem Pfizer-BioNtech has thus adapted its first vaccine (Comirnaty) against the Wuhan strain for the arrival of Omicron. It now offers a booster dose of a bivalent vaccine “Omicron BA.1”, which contains both messenger RNA (mRNA) of the original Sars-CoV-2 virus, and messenger RNA specific to the Omicron BA variant. .1. This serum was authorized by the European Medicines Agency in early September. Hundreds of millions of doses will be ready this year, Pfizer says.

Spikevax, the vaccine from American biotech Moderna, has also been adapted in the form of a bivalent vaccine against BA.1, on the same principle as that of Pfizer. This “Omicron BA.1” serum was approved in Canada as well as by the European Medicines Agency at the beginning of September.

In addition to Moderna and Pfizer/BioNTech, other bivalent vaccines are in the works. This is particularly the case of a vaccine candidate from the French and British laboratories Sanofi and GSK targeting the Delta and Beta strains.

The arrival of the BA.4 and BA.5 sub-variants

The laboratories are working on other bivalent vaccines specifically targeting, in addition to the original strain, the sub-variants of Omicron, BA.4 and BA.5, which have become dominant.

For Europe, Pfizer and BioNTech have a head start. At the end of August, they received emergency authorization from the FDA for their bivalent vaccine against BA.4 and BA.5. They also received the green light from the European Medicines Agency on September 12.

For its part, Moderna has also developed a bivalent vaccine targeting BA.4/5: the latter is currently only approved in the United States, not yet in the European Union. Moderna explains, however, that its bivalent Spikevax serum against BA.1 “demonstrates […] also a higher response against the Omicron BA.4/5 sublines compared to the first generation vaccine. But in the absence of complete clinical data, Professor Antoine Flahaut, director of the Institute of Global Health at the University of Geneva, says he is cautious about the “superiority” of new bivalent vaccines compared to the first formulas.

Which vaccines for the fall campaign?

France has made orders for several million Wuhan / BA.1 and Wuhan / BA.5 bivalent vaccines from Pfizer / BioNTech and Moderna, according to the Directorate General of Health. These doses will be made available to pharmacies and vaccination centers as soon as the High Authority for Health (HAS) has issued its opinion on the place of these new vaccines in the French vaccination strategy.

Orders from the Sanofi (monovalent Beta) and Spanish Hipra (bivalent Alpha-Beta) laboratories, whose vaccines are still being studied by the European Medicines Agency, have also been placed, but are not expected before the end of the year, specifies the DGS.

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