Montreal seroprevalence study | Nearly one in ten children already infected last summer

Nearly 10% of Montreal children under 12 had already been infected with SARS-CoV-2 last summer, compared to 6% last winter, according to a new study from the University of Montreal and the ‘McGill University.

Mathieu Perreault
Press

By comparison, 15% of adults had already been infected last winter, according to data from Héma-Québec. These are seroprevalence blood tests, which detect antibodies generated by infection with SARS-CoV-2, the coronavirus responsible for COVID-19. Seroprevalence can be caused by a vaccine, but 12-year-olds cannot receive the one against COVID-19.

Infections were almost three times higher in Montreal North than in the West Island.

“It confirms that social inequalities play an important role in the impact of the pandemic,” explains Kate Zinszer, epidemiologist at the University of Montreal and lead author of the study.

Does the lower infection rate in children than in adults mean that children are a less important vector of transmission, unlike with influenza, for example? “It’s possible, but we can’t be sure with this data. There may be other factors, for example confinement after a case is detected in a school. ”

The study first analyzed the seroprevalence in Montreal children between October 2020 and March 2021, then between May and August 2021. The Héma-Québec study on seroprevalence in adults took place between January and March 2021.

The team of M^me Zinszer also measured seroprevalence in adolescents. Another striking fact from the study is that adolescents were more likely than children to have been infected in the winter of 2021, but less so in the summer of 2021. However, adolescents began to be vaccinated last spring, and vaccination can also create antibodies against SARS-CoV-2. They should therefore have had a much higher seroprevalence rate than that of children under 12 years of age. “This poses very important questions on the participation of Montreal adolescents in vaccination and on their behaviors facilitating the transmission of SARS-CoV-2, which will have to be deepened,” says the Montreal epidemiologist.

Girls and boys

The study of M^me Zinszer also finds that in children, girls are 30% more likely to be infected than boys. “These are not statistically significant results, but one wonders if there are different behaviors in girls and boys. ”

As childhood immunizations are imminent, the study authors ask parents to bring their children for a blood test in order to have seroprevalence data before immunization, so that results reflect infections, not vaccination. Why not have started the third data collection earlier? “There have been all kinds of brakes, announcements, new measures; research is complicated, says M^me Zinszer. The first data collection was also delayed by a threat of a strike by teachers. ”