Omicron is the least well recognized variant
In order for the immune system to engage in battle, it must first be able to recognize the intruder. However, the level of antibodies measured in the blood plasma of doubly vaccinated participants in the study shows that their immune system struggles to recognize the Omicron variant.
Indeed, the surface proteins of the Omicron variant were less well recognized by the antibodies of vaccinated people than the surface proteins of the Alpha, Beta, Gamma and Delta variants, observed Andrés Finzi, researcher at the Research Center of the Center hospitalier de Université de Montréal (CHUM), in a new study pre-published on the medRxiv website.
But what level of antibodies is required to be able to say that a person will be able to effectively fight the virus? “This is the problem we have had since the start of the pandemic, we cannot establish it”, says Dr Gaston De Serres, from the Institut national de santé publique du Québec (INSPQ), who also participated in the study.
Vaccinees who have had COVID-19 remain the best protected
The study compares two cohorts: doubly vaccinated people who have never been exposed to SARS-CoV-2 and doubly vaccinated people who have had COVID-19.
It does not matter when this infection occurs: whether it occurred before vaccination, between the two doses or after the second dose, the infection acts as a “third stimulation of the immune system”, and the results show that this cohort recognizes better Omicron than other vaccinees.
Why ? “When we are infected, our immune system is exposed to the whole virus. Vaccination, on the other hand, targets the surface protein of the virus, the spicule, ”recalls Dr.r Gaston De Serres. The fact of having already rubbed shoulders with the SARS-CoV-2 virus, regardless of the variant, still seems to give this cohort a small advantage over double vaccines who have never contracted COVID-19.
Since the start of the pandemic, more than 500,000 Quebecers have contracted COVID-19. About 78% of the population received two doses of the vaccine.
Too early to know if the long interval between the first two doses will have an effect
Another element of comparison used in the study: that between people doubly vaccinated with a short interval (4 weeks) and those doubly vaccinated with a long interval (16 weeks).
In Quebec, most people who have been vaccinated twice have been vaccinated with an interval varying between 8 and 16 weeks. Studies published in the fall by the INSPQ showed that an interval of at least 8 weeks between the two doses reinforced protection against the Delta variant.
Will the long gap offer the same advantage against Omicron? The first results so far show a better performance of the long interval to neutralize Omicron. “But it is too early to confirm this,” says Finzi. “It’s an interesting trail,” says Dr From Serres. “But of course, it’s still unclear whether that makes a big difference to the actual protection against the virus. ”
Three doses are better than two
This is the element on which the researchers insist. The third dose, “it is clearly useful,” says Dr From Serres. “We know that the level of antibodies will be increased considerably compared to the second dose. ”
And while the antibodies generated by the vaccine will not be as precise as those that have faced the virus as a whole, they will likely be large enough to overcome Omicron.
As of Monday, people aged 60 and over can make an appointment for their third injection. An interval of at least three months between the administration of the second and the third dose is recommended.
Certain groups are also eligible for the third dose, including immunosuppressed people, healthcare workers, first responders and pregnant women.
With the collaboration of Alice Girard-Bossé, Press