Ontario is set to experience a fourth wave of COVID-19, according to Dr. Colin Furness, an infection control epidemiologist at the University of Toronto.

"There is no doubt we will face a fourth wave in the fall," Furness told Narcity in an email. "It will be sparked by a resumption of indoor gatherings in [step three]." Indoor get-togethers of up to 25 people are permitted in step three, as well as indoor fitness and dining with capacity restrictions.

Furness believes that the fourth wave "will be almost entirely experienced by unvaccinated people," and will consist of "sporadic, intense outbreaks, harder to anticipate or predict." He says that overall case counts could get quite high.

Ontario can curb the impact of the fourth wave by limiting indoor gatherings and continuing to vaccinate residents. "A third booster shot in the winter or early next year to improve effectiveness against emerging variants seems likely to me," he added.

In a recent interview with Narcity, Furness explained that the Delta variant is about "50 or 60% more transmissible than [the Alpha variant, which is] 50 or 60% more transmissible than the original strain. So you're more than twice as likely to get infected in a given situation."

He believes that the rest of Canada will also experience the fourth wave, which will "driven by and suffered by" unvaccinated Canadians from coast to coast.