July 7, 2022

Faced with Omicron, are the vaccines effective?

COVID-19 – More contagious than Delta, Omicron is spreading at a rapid pace. Faced with this variant which “reshuffles the cards”, Gabriel Attal hammered, this Tuesday, December 21, that “a third dose protects” against Omicron. In a study published the day before, the Pasteur Institute questioned the effectiveness of vaccines as well as monoclonal antibody treatments against this variant which risks rapidly becoming the majority in France. The results show encouraging data, although uncertainties persist.

Why is Omicron worried?

“In South Africa [où il a été détecté pour la première fois en novembre, comme au Botswana, NDLR], the Omicron variant replaced the other viruses in a few weeks and is responsible for a sharp rise in the number of diagnosed cases ”, note the researchers of the Pasteur Institute, specifying that“ analyzes ”carried out“ in different countries indicate that the doubling time of cases is about 2 to 4 days ”.

Proof of this fulgurance: Omicron is now largely in the majority in new contaminations in the United States, where it represents 73.2% of cases during the week that ended on December 18, according to data transmitted by the American health authorities on Monday evening. The previous week the figure was only 12.6%.

In France, Gabriel Attal said on Tuesday that Omicron now represents 20% of positive cases identified in France.

Against Omicron: two, three or even four doses?

“The researchers conclude that the many mutations present in the Spike protein [qui permet au Covid-19 de pénétrer dans nos cellules, NDLR] […] allow it to largely escape the response of the immune system ”, underlines the Institut Pasteur.

The bad news is that compared to Delta, more antibodies are needed to fight Omicron (“5 to 31 times more antibodies to neutralize Omicron, compared to Delta, in cell culture tests. ”, Details the study).

Two doses of vaccine would not provide adequate protection against Omicron. Indeed, during their study, the researchers found “that the blood of patients who had Covid-19, collected up to 12 months after symptoms, as well as people who received two doses of the Pfizer vaccine or AstraZeneca vaccine hardly neutralizes the Omicron variant, five months after vaccination ”.

The good news is that the vaccine booster appears to be effective, as the government has recalled. “The sera from individuals who received a 3rd Pfizer booster dose, analyzed one month after injection, remain effective against Omicron”, note the researchers. “You have to have this third dose to be protected against Omicron, to be protected against severe forms”, insisted on Tuesday on BFMTV the deputy director of the National Reference Center for respiratory viruses at the Institut Pasteur, Vincent Enouf.

The professor however recalled that the third dose, the protection of which is effective “between a week and 10 days” after inoculation, does not prevent “being a carrier of the virus” or “having a small symptomatology” like “A cold”, insisting on respecting barrier gestures.

The duration over time of protection from the third dose remains one of the major unknowns in the study. For Professor Vincent Enouf, “it is possible that we will be vaccinated again so as to update our antibody portfolio because we will either have this variant, or possibly another”.

It remains to be seen whether new specific vaccines will still be needed to counter Omicron. Emer Cooke, director of the European Medicines Agency (EMA), stressed on Tuesday “that there is no answer to the question yet”, whether for Omicron or a possible next variant. But vaccine manufacturers are already working on the issue, as Novavax recalled on Monday, whose Nuvaxovid serum was the last to be approved in the European Union but which had been tested in clinical trials when the Alpha and Beta were dominant.

Is Omicron resistant to monoclonal antibodies?

If the vaccine booster seems to provide good protection against Omicron and particularly severe forms of Covid-19, the same would not apply to monoclonal antibody treatments. During their study, scientists from the Institut Pasteur screened nine of these synthetic antibodies “used in the clinic or in the preclinical development phase”.

Result: “six antibodies completely lose their antiviral activity, and the other three are 3 to 80 times less effective against Omicron compared to Delta”, demonstrates the Institut Pasteur.

Omicron “has acquired marked resistance to antibodies,” comments Olivier Schwartz, co-author of the study and director of the Virus and Immunity Unit at the Institute. “Currently available anti-SARS-CoV-2 therapeutic monoclonal antibodies are mostly inactive.”

See also on The HuffPost: Covid: The variant discovered in South Africa worries researchers but your priority is elsewhere