From Saturday, Quebecers will once again be able to share the microphone in bars to sing their favorite nostalgic tune and will no longer have to present their vaccination passport when entering the cinema. However, despite the reassuring speech of the health authorities on the effectiveness of the booster dose, it is the triple-vaccinated who have been the most hospitalized in Quebec for more than a month.
Of the 40 new COVID hospitalizations recorded in the province for the day on Sunday, 26 had received a booster dose, compared to six who were not vaccinated. This trend is also present among the number of COVID-19 infections in Quebec.
Less than a month after the administration of the majority of the third doses, is this a sign that the booster dose no longer confers the hoped-for protection? The simple answer is no. The explanation behind it, however, is quite complex.
First, the vaccination campaign for this third dose began at the beginning of last fall for people at risk, especially the elderly. By mid-February, when the triple-vaccinated began to outnumber the unvaccinated in hospitals, it had therefore already been about four months since the booster doses were administered for these older patients. vulnerable.
However, the protection conferred by the infection and the vaccine seems to diminish over time. “Over a period of four months, we know that the effectiveness is maintained better for serious problems, explains Nicholas Brousseau, medical advisor at the National Institute of Public Health of Quebec (INSPQ) and president of the Committee on Immunization of Quebec. But to avoid any infection, even a very mild COVID that resembles a cold, the duration of effectiveness of the booster dose does indeed seem to decrease more quickly. »
The difference of the Omicron variant compared to the original virus is also substantial, notes Benoit Barbeau, professor of biological sciences at the University of Quebec in Montreal (UQAM). “We know very well that the booster dose offers us protection, but it decreases more quickly against Omicron than with the Delta variant. Not only is the virus more infectious, but in addition, the vaccine formulation of the booster dose was above all adapted to the original virus. »
An INSPQ study published in mid-February assesses the effectiveness of the third dose at 90% against more serious forms of the disease, compared to 80% for two doses of vaccine.
A risk with variable geometry
Beyond the efficiency which decreases over time, the question of age is central to explaining the change of course in the composition of hospitalizations since the beginning of the year. “The elderly are the most at risk of being hospitalized, period. But in addition, once they are infected with COVID-19, the risk of complications is higher, underlines Benoit Barbeau.
It is for this reason that it is relevant to observe hospitalizations by age: last Monday, there were 238 people under the age of 60 hospitalized for COVID-19 in Quebec, compared to 1,014 aged 60 and over, i.e. 81%.
Their perception of the risk is, rightly, greater, which explains why it is the segment of the population most inclined to seek a third dose of vaccine. As of March 7, 85% of adults aged 60 and over had rolled up their sleeves for the third time, compared to an average of 55% among Quebec adults.
The most vulnerable people, therefore those who find themselves in greater numbers in hospitals, are thus those who are most widely vaccinated, which forms a distortion, according to Nicholas Brousseau.
The reaction of the elderly to the booster dose is also different; it is less strong, and therefore less effective, than in a younger adult, explains the INSPQ’s medical advisor. “Older people will return more quickly to a threshold where they are more prone to being infected and possibly hospitalized. That’s why we already hear about a second booster dose. »
Countries like Israel, Chile, Spain, Denmark and Sweden offer the fourth dose to certain risk groups. In Quebec, it is only offered to immunosuppressed people.
Even if a reflection is underway, Nicholas Brousseau affirms that there is no question for the moment of extending the fourth dose to a wider public given the effectiveness of the third dose against the complications of COVID -19.
A question of proportions
Although they show a new trend emerging, the hospitalization data in absolute numbers does not reflect the proportion of each group in the population. “We can still see that the two curves are getting closer, notes Benoit Barbeau, but the fact remains that the non-vaccinated are the people who are the most likely to be hospitalized. »
Thus, in relation to their demographic weight, it is still the non-vaccinated who form the largest group among hospitalizations, with a rate of 2.1 per 100,000 people on March 5. Rather, among the triple-vaccinated, there are 0.4 hospitalizations per 100,000 people.
“If 100% of Quebecers were vaccinated, well 100% of people who would be hospitalized would be vaccinated. Should we therefore conclude that vaccines are not effective? Of course not,” says Benoit Barbeau.
“We are not immune to a sixth wave”
The question of the duration of the protection offered by vaccines against COVID-19 remains relevant, since the government intends, “by mid-April at the latest”, to withdraw the obligation to wear a mask in public places (except in public transport), one of the last stages of deconfinement according to the government.
While the two experts believe now is a good time to end health measures, they believe it’s quite likely the province will see an increase in cases and hospitalizations in light of new data revealed by The duty.
“Whether it is to remove the masks or to increase the number of people who are allowed in a place, it is certain that the risks of transmission, infection and even reinfection are higher”, admits Benoit Barbeau.
But the key is still and always the same, according to Nicholas Brousseau: “go there as gradually as possible, find a balance between returning to a normal life without deconfining too quickly, then staying on the lookout, because we are not sheltered from a sixth wave”.
The INSPQ’s medical advisor recalls, however, that the Omicron wave occurred in the middle of winter, when families and friends gathered inside, well sheltered from the snow, to celebrate Christmas. “This time, we will not be offering such good conditions for the virus to be transmitted. Most people will be outdoors. »