A majority of Quebecers have hybrid immunity to COVID-19, but new variants this fall could cause an upsurge in cases and hospitalizations, and even have a greater impact than the arrival of Omicron if the mutation escapes to hybrid immunity.
This was highlighted Thursday by the Institut national de santé publique du Québec (INSPQ) based on hypothetical scenarios for Greater Montreal examined by its experts and those of the Research Group in Mathematical Modeling and Related Health Economics. in infectious diseases from Laval University.
According to the INSPQ, the evolution of the epidemic will depend mainly on the maintenance of this hybrid immunity, but also on the characteristics of potential new variants.
The rise in cases and hospitalizations by winter 2023 could be “limited” if the arrival of a new variant is still countered by hybrid immunity.
However, a new variant that evades hybrid immunity — “with a level of escape similar to that of Omicron compared to Delta” — could cause a much larger upsurge in cases, to the point of surpassing that of the wave. Omicron, says the INSPQ Thursday in a press release.
According to the organization, “a significant amount of hospitalizations could result, even if the variant is not more severe than Omicron and the protection offered by hybrid immunity is high against hospitalizations”.
The analyzes identify three key elements that emerge from the two years of the pandemic: the fall and the holiday season are periods conducive to an upsurge in cases; people who are both vaccinated against COVID-19 and who have also been infected with the virus (hybrid immunity) enjoy better protection against future infections and the latest waves have been caused by new variants.
However, it is pointed out, the virus continues to mutate and Quebec is not immune to new variants that are more transmissible or that escape the different types of immunity, including hybrid immunity.
These scenarios produced using mathematical models were carried out to support the work of the authorities in anticipating the long-term evolution of the COVID-19 epidemic in Quebec.
“It is currently impossible to predict when a new variant […] could arrive in Quebec and what its characteristics would be,” explains Marc Brisson, director of the Université Laval research group.
On the other hand, we know that Omicron and its sublines, which are more contagious, but less severe, have caused a paradigm shift in the evolution of the epidemic, adds the researcher.
Also, it is pointed out that the uncertainties concerning the efficacy of a new bivalent vaccine and the characteristics of a potential new variant are currently too great for the modeling to be able to estimate an optimal moment of vaccination with a booster dose.