Héma-Québec seroprevalence study | More than one in four adults infected with COVID-19 during the winter

More than one in four adults in Quebec contracted COVID-19 in the winter, between December and March, a new seroprevalence study published Monday by Héma-Québec reveals. This is the agency’s fourth major investigation since the pandemic began two years ago.

Posted at 5:00am

Henri Ouellette-Vezina

Henri Ouellette-Vezina
The press

Alice Girard Bosse

Alice Girard Bosse
The press

“We are not surprised at all. In our personal lives, we all know someone who has recently become infected with Omicron. And it didn’t go down during the first three months of the year,” says the Dr Marc Germain, Vice President Medical Affairs and Innovation at Héma-Québec, in an interview with The press

It is exactly 27.8% of adults who have contracted the virus during the winter season. During the first wave, this was barely 2.2%. Also, a new serological survey will be conducted “in the coming weeks” to take into account the entire sixth wave, powered by the BA.2 variant. “It is already clear that we will be above 30%,” confirms the Dr Germain.

Essentially, the study — conducted on just over 1,600 blood donors in January, February and March — found that the Omicron wave affected more than a third of people in Greater Montreal and about a quarter in the regions.

It is mainly the over 40s who contracted the virus in the metropolis, during the fifth wave. As many as 70% of people aged 18 to 40 living on the island of Montreal or in its crowns are said to have contracted it between December and March.

“It’s impressive because we’re really talking about evidence of recent infections, which appeared during the Omicron wave. And when we talk to our colleagues from Public Health, it doesn’t conflict at all with other estimates they make on their part,” explains the D.r Germain on the subject, stating that the risk of reinfection remains very real.

Drop in blood donations

In addition to these numbers, Héma-Québec reminds us that it is still difficult to bear the consequences of the sixth wave of COVID-19.

The organization says “it is having trouble meeting its weekly goals due to cancellations.”

As early as early April, nearly 20% of blood donations were canceled on certain days, representing “abnormally high” cancellation rates.

“This concern is very real, especially since with the summer period — and it was before the pandemic — it’s much harder to convince people to take the time to come and donate blood,” said Dr.r Germain, who calls on the population in a position to mobilize to donate blood.

In particular, we recommend that users check availability by going to a donation office, even if in theory this only works by appointment. The organization estimates that every 80 seconds a person needs a blood donation in Quebec. The hospital network needs about 1,000 donations per day to meet the needs.

A challenge with vaccination

Since the start of the pandemic, Héma-Québec has measured participants for the presence of antibodies to protein S, present on the surface of SARS-CoV-2. If blood tests showed these antibodies, the person was likely infected with the virus.

“When our bodies come into contact with the virus, our immune system develops antibodies against different parts of the virus,” says Dr.r Gaston De Serres, Chief Physician of the Immunization Division of the National Institute of Public Health of Quebec (INSPQ).

However, the situation has become more complicated with the advent of the vaccine. Since vaccination also leads to the development of antibodies against protein S, it then became impossible to distinguish the antibodies elicited by vaccination from those produced by infection. The experts therefore had to choose a different protein to target. Their choice fell on the nucleocapsid, because the antibodies it induces are only present in people infected with the virus.

However, this choice of protein presents a new challenge. Indeed, the antibodies that the nucleocapsid induces are much less durable than those against the previously used surface protein.

“We can get a good idea of ​​recent infections, but we have no information on the number of people infected since the start of the pandemic,” explains Dr.r From Serres.

Nevertheless, these seroprevalence studies prove to be very helpful to public health authorities, argues Dr.r From Serres. “It’s really important because we use it for different purposes,” he says.

First, these studies allow to implement the best possible vaccination strategies depending on the immunity conferred on the population. The information also confirms the models predicting the evolution of the pandemic. “What we saw with the Omicron wave confirmed [l’efficacité de] our models of the evolution of the pandemic. The ministry, government and public health authorities can therefore have confidence in our forecasts,” he concludes.

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