Ontario well into 6th wave driven by BA.2 subvariant, uncertainty over COVID case growth: science table
Posted April 14, 2022 7:45 am.
Last Updated April 14, 2022 8:29 pm.
Ontario’s COVID-19 Science Advisory Table released new COVID-19 modelling on Thursday, confirming that the province is well into the sixth wave while suggesting that there remains considerable uncertainty over case growth.
The science table published updated modelling for the first time in weeks, concluding that the sixth wave has been driven by the highly contagious BA.2 subvariant, waning immunity, and the lifting of public health measures.
While the latest wastewater surveillance data on the advisory table’s dashboard indicates the spread of the virus has either plateaued or is now in decline, Ontario’s science table says there is “significant uncertainty” around the impact of case growth on the provincial health system and deaths, noting that modelling indicates hospital occupancy is likely to continue to rise for some time.
“COVID-19 infections in healthcare workers are as high as in the last Omicron wave,” the science table wrote. “High infection rates combined with potentially high hospitalization rates will reduce Ontario’s ability to provide care for non-COVID-19 patients.”
The modelling suggests hospitalizations and ICU admissions will continue rising but it’s unlikely they will reach levels seen earlier this year during the fifth wave of the pandemic.
The group says COVID-19 infections among healthcare workers, are as high as they were during the Omicron wave, and that combined with rising hospitalization numbers may impact healthcare capacity.
Ontario’s COVID-19 Science Advisory Table also urges anyone with Omicron symptoms to stay home and self-isolate. These individuals must produce at least two negative rapid antigen tests separated by at least 24 hours “to be confident that an individual is not infected.”
They also note that masking in indoor areas will substantially reduce the risk of getting and spreading.
The science table defines Ontario’s COVID-19 wastewater signal as a “weighted mean of standardized, biomarker-normalized concentrations of SARS-CoV-2 gene copies across 103 wastewater treatment plants, pumping stations and sewer sheds in the 34 public health units.”
Wastewater samples are typically taken three times per week at each location. The science table says there is a five to a seven-day lag between the detection of SARS-CoV-2 gene copies in the wastewater and the diagnosis and reporting of COVID-19 cases.
The science table says the dotted orange line and the lighter shaded area represent incomplete data (less than 90% of data available on a given date.) Photo: Ontario COVID-19 Science Advisory Table.
Part of the reason for the transmission slowing could be a built-up immunity in the population due to the vast number of individuals who have had an infection in recent months.
The science table concludes that Ontario’s wastewater signal may have crested but stress that it is still uncertain whether the current plateau will
remain or be followed by an increase after the holidays, or a decrease.
University of Toronto epidemiologist Colin Furness warns the spread of the virus creates some public immunity but it does not make the virus go away. Furness points to the U.K. where 97 per cent of the population has Omicron antibodies yet infections continue to spread.
“You would think that would be enough for herd immunity, it would have to be enough for herd immunity,” said Furness on the Big Story Podcast. “And yet what we are seeing in the U.K. right now is record levels of hospitalization.”
The science table determined that the BA.2 Omicron subvariant became dominant in Ontario around March 10.
The most important symptoms of Omicron, according to the science table:
- Headache
- Runny nose or sneezing
- Sore throat
- Cough
- Fever
- Gastrointestinal symptoms
- Loss of smell
Health officials and members of the science advisory table continue to strongly encourage mask-wearing while indoors. The science table notes that recent studies from the United States analyzed the impact of masking policies on SARS-CoV-2 community transmission. Mandatory masking reduced the incidence of SARS-CoV-2 infection consistently, it concluded.
Omicron variant in Ontario. Photo: Ontario COVID-19 Science Advisory Table.
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Hospitalizations are still expected to rise in the weeks ahead
The head of the Ontario Hospital Association (OHA) is warning that even though infections may have peaked the province will likely still see a rise in hospitalizations for up to two weeks.
“I expect we have another week or two of rising COVID hospitalization still ahead,” said OHA President Anthony Dale on Twitter. “A tough period is still ahead with so many staff absences due to uncontrolled community spread.”
Many hospitals in the province are facing significant staff shortages because of COVID-19 and Dale says the rise in hospitalizations in recent weeks has impeded the ability of hospitals to operate normally.
Some hospitals, including the Kingston Health Sciences Centre, have had to cancel recent surgeries due to a surge in the virus.
Provincial officials reported 1,332 COVID patients in the hospital on Wednesday, up from nearly 25 per cent one week ago. The number is down slightly from the 1,366 on Tuesday when the province saw the highest number of hospitalizations since Feb. 16.
The number of COVID-19 patients in the ICU sits at 182 and is down from 190 a day ago but up from 168 one week ago. There are 85 patients on a ventilator.
New Omicron XE variant detected in Canada
Six cases of the new Omicron XE variant have been detected in Canada.
The new variant is being described as the most transmissible strain so far with early estimates suggesting it is 10 per cent more infectious than BA.2 but does not appear to result in more serious illness.
Canada’s chief public health officer Dr. Theresa Tam says the new variant is a combination of genetic material from Omicron and the BA.2 variant and transmission within the country would not be a surprise.
“We do expect that to happen because there is a lot of transmission of this virus all over the world,” she says. “We’re watching that one very carefully.”
The World Health Organization (WHO) warns that early findings on XE require further confirmation.
