Although two-dose vaccination still likely provides good protection against severe forms of COVID-19 induced by the Omicron variant, administering a third dose is becoming more important than ever to curb the spread of this variant which, spreading like wildfire, could increase the pressure on the health system and essential services.
If, to date, Omicron does not appear to be more dangerous than the Delta variant, its very high transmissibility risks multiplying infections to the point where vulnerable and unvaccinated people could invade or even saturate hospitals, and where the number of infected people. quarantines could seriously disrupt the services offered in hospitals, schools and other essential places of society.
It is not yet clear whether Omicron can cause severe symptoms, as so far it has mostly infected young people, already immune from a previous infection or from a vaccine, in countries in southern Africa, notes Marc-André Langlois, director of the University of Ottawa’s Coronavirus Variant Rapid Response Network. However, knowing that advanced age and obesity – two predisposing factors to a severe form of COVID-19 – are much more common in Canada than in Africa, we can imagine that if people who are not vaccinated have also overweight and elderly, infection with Omicron would have significant effects. There is a high probability that these people will have symptoms as severe as those caused by the Delta variant, he explains. “And as about 10% of our population has not been vaccinated, we can apprehend an overflow in our hospitals, which will no longer be able to offer surgery and cancer treatment services. “
Efficiency under the microscope
The effectiveness of vaccines in protecting us against Omicron is currently being evaluated by many researchers. Two renowned teams in the field made public in pre-publication (that is to say before peer review) the results they obtained in the laboratory after putting the Omicron variant in the presence of the plasma of people who had received two doses. mRNA vaccine, in particular.
In both studies, the level of antibodies capable of neutralizing the Omicron variant was low or even below the detection limit in plasma in a significant proportion of people who were doubly vaccinated, which resulted in very little neutralization of the Omicron variant. “The decrease in the effectiveness of antibodies could explain the large number of re-infections and infections after vaccination,” say researchers from the Institut Pasteur.
However, it should be noted that these two studies were carried out with the plasma of people who received their first two doses of vaccine within a four-week interval, while in Quebec, the time between the two doses was extended to eight weeks. And this extended lead-time has been shown to provide better, longer-lasting protection against all variants circulating up to Omicron.
In contrast, in people who received a booster dose, Omicron neutralization was up to 154 times higher, according to researchers at Rockefeller University.
Despite very high levels of antibodies, the serum of these people had a neutralizing efficacy of 5 to 31 times less against Omicron than against the Delta variant, specify the researchers of the Pasteur Institute.
All the same a valid lead
Even if the antibodies produced after the reception of a third dose are not as effective, their quantity is such that they will probably succeed in countering the infections, underlines the specialist in immunology Benoit Barbeau, of the UQAM. And since Omicron is highly transmissible, preventing infections would go a long way in limiting the damage. “Because the proliferation of cases of infection will inevitably result in an increase in hospitalizations, even if the proportion of infected people who develop severe forms is lower,” he says.
“Right now, the strategy is to stop the transmission of this variant because if healthcare workers do get the infection they will have to quarantine themselves until they test negative.” , and it will be the same in the schools. If the Omicron variant spreads too much, workers essential to the proper functioning of the company will have to be absent, ”emphasizes Mr. Langlois.
The third dose has several positive effects: it increases antibodies, which in turn can reduce transmission by neutralizing viruses before they infect our cells, and it increases the immune response, helping to prevent severe symptoms of the disease. More precisely, it increases the number of immune cells capable of recognizing the virus, including T cells, these sentinels which will identify infected cells and eliminate them, and B cells, which will produce new antibodies.
“And we must not forget that it is almost the holiday season, we will meet in gatherings, nobody wants to transmit the virus to vulnerable people during Christmas. Getting your third dose now, before the holidays, is a very good idea, ”advises Dr.r Langlois, who recommends that this booster dose be given to all adults 18 years of age and over.