MONTREAL — About 125,000 people in Quebec aged 18-69 are estimated to have contracted COVID-19, according to a new study published Wednesday by Quebec's blood collection agency — more than three times the official number reported by health authorities.
But the Hema-Quebec study indicates the majority of Quebecers remain vulnerable to being infected by the novel coronavirus, agency vice-president Dr. Marc Germain said.
"The conclusion is obvious," Germain said in an interview Wednesday. "It's a very small proportion of the population who have been exposed to the virus during the first wave. And that means there are many people in the population who are susceptible to being infected."
It also means Quebec is far from developing what's known as a natural or herd immunity against the virus, said Dr. Gaston De Serres with Quebec's institute for national health, which collaborated on the study.
So-called herd immunity occurs when enough of a population has contracted a virus and developed an immune response to it, helping to prevent them from getting reinfected and transmitting it. "With this data, it shows that herd immunity in Quebec is not present," said De Serres. "Forget it."
Germain noted the increased case numbers mean the death rate from COVID-19 is far lower than portrayed in official figures. Germain said while it's encouraging that the "vast majority" of people infected with COVID-19 survive, "we can't forget there is still a significant amount of death. This is not a benign disease."
Quebec reported 155 new COVID-19 cases Wednesday, bringing the total number of people with confirmed infections to 60,000. The province also reported two additional deaths attributed to the novel coronavirus, for a total of 5,687.
Hema-Quebec's antibody study involved a sample of 7,691 people aged 18-69 who donated blood between May 25 and July 9. It revealed 2.23 per cent of donors had been infected with COVID-19. The study indicated the highest rates of infection were found in Montreal and Laval, with just over three per cent, while in most of the rest of the province the rate was much lower at 1.29 per cent.
Researchers extrapolated that about 124,880 people in the same group were infected across the province. Health authorities, meanwhile, had reported about 37,000 cases for the 20-to-69 age group during the same period.
Germain said the study sample was likely representative of the general population because "there is no fundamental difference regarding the susceptibility of infection between someone who comes to give blood versus someone taken at random from the public."
De Serres explained the study is not complete. Everyone who donated blood and tested positive will be called in the coming weeks by Hema-Quebec to determine whether they felt symptoms, with results expected by the end of August.
The key to managing the pandemic, De Serres said, is to know how many people infected with COVID-19 are symptomatic.
"The higher the number of asymptomatic people, the more difficult it is to control the pandemic," he said, explaining that people who don't feel sick are less likely to be careful about hygiene or to get tested.
Wednesday's study is part of a series of COVID-19 research produced by Hema-Quebec. The agency recently studied the plasma donations of 15 people who recovered from COVID-19 and concluded the concentration of antibodies developed to fight the virus declined over time. In some cases, Germain said, they disappeared.
"But does that mean there is no protection? Not necessarily," he said, adding that a person's immune system has other ways of protecting someone from being reinfected.
But the doctor said he is not particularly worried that people who have recovered from COVID-19 are looking at a reactivation of the disease years down the road, as is the case with those who catch such viruses as chicken pox or herpes.
Given what scientists know about coronaviruses and what researches already know about COVID-19, he said, "I'd be very, very surprised if we discover all of a sudden, in many years, that a good number of people have a chronic infection or reactivation."
This report by The Canadian Press was first published Aug. 5, 2020.
Giuseppe Valiante, The Canadian Press