COVID-19 variants will impact herd immunity, Ontario official explains

Elisabetta Bianchini
·4 min read

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Dr. Barbara Yaffe, Ontario’s associate chief medical officer of health, explained on Thursday that with the emergence of more COVID-19 variants that are more transmissible, a larger number of people need to be vaccinated to achieve herd immunity.

“The doubling time for cases will be much lower, cases will be spread more quickly,” Dr. Yaffe said. “To get herd immunity, my understanding is with a non-variant strain we’re looking at 60 to 70 per cent coverage of the population, and I’ve understood that we may need more like 70 to 80 per cent with a variant strain.”

“We would need more...population coverage to achieve herd immunity.”

To date, Ontario has confirmed 15 cases of the more transmissible B117 COVID-19 strain, first identified in the U.K.

Dr. Yaffe shared that the provincial lab has done a point prevalence study, assesses sample of positive COVID-19 cases on a certain date, to see if there is evidence of a variant of concern.

Six cases of the COVID-19 variant have been identified in a Barrie, Ont., long-term care home. A total of 55 people became ill within 48 hours of the first COVID-19 case being identified.

“At this time we know that there’s a very high probability that the mutation identified is a variant strain of concern,” Dr. Yaffe said.

Dr. Dirk Huyer, coordinator of the provincial outbreak response, confirmed that there have been 769 reported outbreaks in the past seven days, 1,290 in the past 30 days. About 50 to 60 per cent of those outbreaks have been reported in vulnerable settings like long-term care homes, retirement homes, hospitals and group homes. The next most common outbreak locations are work places.

‘Schools should be the last doors to close and the first to open in society’

The Hospital for Sick Kids in Toronto released a guidance document about school operations during the COVID-19 pandemic, which stresses the negative impacts of prolonged school closures.

The core recommendations for keeping schools environments safe include:

  • Testing recommendations for symptomatic and exposed students and additional considerations for asymptomatic testing

  • More robust physical distancing and non-medical mask use, particularly for high school and middle school students in the highest risk regions

  • Emphasis on cohorting rather than strict enforcement of physical distancing for younger students because of the centrality of play and socialization to their development and learning

  • Updated section on mental health awareness and support for all children and youth

“When considering public health measures aimed at curbing community transmission of COVID-19, it is our strong opinion that schools should be the last doors to close and the first to open in society,” a statement from Dr. Ronald Cohn, president and CEO of SickKids and co-author of the document reads.

“The current school closures need to be as time-limited as possible. It is therefore imperative that bundled measures of infection prevention and control and a robust testing strategy are in place.”

Dr. Yaffe said the province “definitely” wants kids in schools but added that it has been a “challenging situation.”

“We found that the rate of positivity in kids had gone up quite a lot just around the holiday period and after the holiday period,” she explained. “There was so much transmission that we felt at that point going into a lockdown it would be safer to keep them at home in the south part of the province.”

“What we need to remember is that we do have a lot of layers of protection in the schools but if the community infection rate is high, that’s where it comes into the schools and it becomes unwieldy for the school, for the health, unit and for the kids and their families, to have kids being sent home and whole cohorts being sent home frequently.”

Schools in seven public health units in southern Ontario will reopen to in-person learning on Monday - Grey Bruce; Haliburton, Kawartha, Pine Ridge; Hastings and Prince Edward Counties; Kingston, Frontenac and Lennox & Addington; Leeds, Grenville and Lanark; Peterborough; and Renfrew County.

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