More than one in four Quebec adults contracted COVID-19 during the winter, between December and March, reveals a new seroprevalence study published on Monday by Héma-Québec. This is the agency’s fourth major investigation since the pandemic began two years ago.
Posted at 5:00 a.m.
“We are not at all surprised. In our personal lives, we have all recently known someone who became infected with Omicron. And it did not go down during the first three months of the year, ”says the Dr Marc Germain, Vice-President of Medical Affairs and Innovation at Héma-Québec, in an interview with The Press.
It is precisely 27.8% of adults who contracted the virus during the winter season. During the first wave, this figure was barely 2.2%. A new serological study will also be carried out “in the coming weeks”, in order to take into account the entire sixth wave, powered by the BA.2 variant. “It is already understood that we will be above 30%”, affirms the Dr Germain.
Essentially, the study – carried out on just over 1,600 blood donors in January, February and March – reveals that the Omicron wave affected more than a third of people in Greater Montreal, and around a quarter in the regions.
It is mainly the under 40s who contracted the virus in the metropolis, during the fifth wave. No less than 70% of people aged 18 to 40 living on the island of Montreal or in its crowns would have caught it between December and March.
“It’s impressive, because we are really talking about evidence of recent infections, which appeared during the Omicron wave. And when we speak to our colleagues from Public Health, it is not at all discordant with other estimates that they make on their side, ”explains the Dr Germain on this subject, specifying that the risk of reinfection remains very real.
Drop in blood donations
Beyond these figures, Héma-Québec reminds us that it is still hard to bear the repercussions of the sixth wave of COVID-19.
The organization says it is “struggling to achieve its weekly objectives, due to appointment cancellations”.
Already, at the beginning of April, nearly 20% of blood donations were canceled on certain days, which represents “abnormally high” cancellation rates.
“This concern is very real, especially since with the summer period – and it was like that even before the pandemic – it is much more difficult to convince people to take time to come and donate. blood,” says Dr.r Germain, who calls on the population who is able to do so to mobilize to donate blood.
In particular, we suggest that users check availability by passing a donation office, even if it theoretically 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 a 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 against protein S, present on the surface of SARS-CoV-2. If blood tests showed these antibodies, the person had probably been infected with the virus.
“When our body comes into contact with the virus, our immune system develops antibodies against different parts of the virus,” says Dr.r Gaston De Serres, chief physician at the Immunization Unit of the National Institute of Public Health of Quebec (INSPQ).
However, the situation has become more complicated with the arrival of the vaccine. Since vaccination also leads to the development of antibodies against protein S, it then became impossible to distinguish the antibodies induced by vaccination from those by infection. The experts therefore had to choose another protein to target. Their choice fell on the nucleocapsid, since the antibodies it induces are present only in people who have been infected with the virus.
This choice of protein, however, comes with a new challenge. Indeed, the antibodies that the nucleocapsid induces are much less durable than those against the surface protein used previously.
“We can get a good idea of recent infections, but we don’t have information on the number of people infected since the start of the pandemic,” explains Dr.r From Serres.
Nevertheless, these seroprevalence studies are proving very useful for public health authorities, argues Dr.r From Serres. “It’s really very important, since we use it for several purposes,” he says.
First, these studies make it possible 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 predictions,” he concludes.