The more the days pass, the more the Omicron variant worries the health authorities. Since its emergence, this South African strain has been considered more contagious than previous versions of the coronavirus. But is this really the case? What do we know about its virulence? Are vaccines effective against this variant? We take stock of the available data.
- The Omicron variant, first identified in South Africa on November 24, could become predominant within weeks or months.
- This South African strain would be more contagious than the Delta variant. For the time being, few data concerning its dangerousness are available.
- Two doses of the AstraZeneca vaccine do not protect us from the Omicron variant and two injections of the Pfizer product would not be sufficient.
- Administration of a third dose is necessary to increase antibody levels.
310. This is the number of confirmed cases of the Omicron variant in France, as of December 16. This strain of Covid-19, which raises fears of a sixth wave, is now circulating in 89 countries, according to the World Health Organization (WHO). This variant, classified as “worrying”, raises fears because of its high number of mutations and its increased risk of reinfection. Over the weeks, several data concerning the contagiousness and the dangerousness of the South African variant are published.
A highly contagious version of the virus
On December 14, Tedros Adhanom Ghebreyesus, Director General of the WHO, reported at a press conference that the Omicron variant was spreading “at a rate we’ve never seen with any other variant.” This information was also shared by the Scientific Council in a notice published on December 16. “The impact of the mutations observed for the Omicron viruses on contagiousness is confirmed, both due to an immune escape linked to the mutations located on the spike protein, and to its increased replicative capacity. Transmission is clearly increased compared to the variant Delta.”
According to the United Kingdom, where the number of cases has now exceeded that of the January 2021 peak, the Omicron variant is between 3.2 and 3.7 times more contagious than the Delta variant. “If it’s 10% of the cases of the Omicron variant today in our country, that means that next week it’s 25 or 30%, and that means that in two weeks it will be the majority”, said in the morning of France Interthe Minister of Health Olivier Véran, on December 18.
Is the Omicron variant more dangerous than the others?
For the time being, scientists do not have precise data concerning the virulence of the Omicron variant. It is thus too early to know if it is more dangerous than the previous strains of the virus.
“We have data from South Africa but the population, younger and less vaccinated (30%), is not comparable with the European population”, clarified, to West France, Jonathan Roux, epidemiologist at the School of Advanced Studies in Public Health in Rennes. He added that he was awaiting data from the UK “where the population is closer to the French population: older and highly vaccinated. We will consolidate this information within 10 to 15 days: which will allow us to project ourselves and know what percentage of people end up hospitalized.”
According to several experts, including virologist Jinal Bhiman of the South African Institute of Infectious Diseases (NCID), interviewed by Sciences et Avenir, this more contagious version of the coronavirus would cause less severe forms than the Delta variant.
Two doses of vaccine are not enough
Several researchers are currently trying to determine if the available vaccines are able to protect us from the Omicron variant. To find out for sure, British scientists carried out a study, published on the medRxiv pre-publication site, December 14. The latter conducted it with 581 people affected by the Omicron variant, 56,439 cases of the Delta variant and 130,867 patients not infected with Covid-19.
The results showed that two doses of the AstraZenena vaccine failed to control the Omicron variant. “Efficacy of the Pfizer vaccine after two doses was estimated at 88%, 2-9 weeks after the second dose. It fell to 34-37%, 15 weeks after the second injection”, can we read in the searches. The researchers found that the Pfizer serum was 75.5% effective two weeks after the booster dose.
A third dose would be effective
French scientists were also interested in the efficacy of the vaccine against the Omicron variant. In works, which have been the subject ofa pre-publication on the bioRxiv website on December 16, they studied the sensitivity of the South African strain to monoclonal antibodies and antibodies present in the blood of people who had been vaccinated or had already been infected with Covid-19.
The researchers observed that the antibodies present in the blood of people infected with the virus or who had received two doses of the Pfizer or AstraZeneca vaccine almost no longer neutralized the Omicron variant, five months after vaccination. In contrast, the research authors noted that a third dose with Pfizer’s formula strongly increased antibody levels and would be effective against the Omicron variant. “However, it takes 5 to 31 times more antibodies to neutralize Omicron, compared to Delta”, the scientists said.
“It is now necessary to study the duration of protection of the 3rd booster dose. Vaccines therefore probably lose strong efficacy against the acquisition of the virus, but should continue to protect against severe forms”, said Olivier Schwartz, co-lead author of the study and director of the Virus and Immunity Unit at the Institut Pasteur.
