All signs suggest COVID-19 transmission starting to rebound in Ontario, modelling suggests

Modelling: COVID transmission rebounding in Ont. Data from Ontario's COVID-19 Science Advisory Table shows case numbers, hospitalizations and ICU admissions have stopped declining.

Ontario should prepare for a moderate rebound in hospital admissions due to COVID-19 between now and May, as all remaining surveillance suggests the Omicron wave has hit bottom and is starting to trend back upwards, new modelling indicates.

With the mask mandate ending in most spaces in four days, and the arrival of the BA.2 Omicron subvariant, hospital ICU occupancy could increase by a third to 300 patients by May, the Ontario COVID-19 Science Advisory Table says.

Overall hospital admissions could return to about 800 by this time, significantly lower than the peak in mid-January where overall admissions testing positive for COVID-19 exceeded 4,100.

On Thursday, ICU occupancy fell below 200 and there were 644 total patients admitted across the province.

The modellers cite wastewater signal data that finds increases in the viral signature found in wastewater treatment plants across the province, in all regions other than Ontario’s north

They also found that test positivity among groups still covered by PCR testing are largely on the rise, as well as in workplace rapid antigen screening programs, which have shown increases since mid-February.

Among people under age 59 who have each had at least 40 PCR tests since March 2020, mostly essential health-care and congregate care workers, positivity has trended upward since the start of February.

This latest model is subject to significant uncertainty, modellers warn.

“There remains uncertainty on current community levels of immunity, future change in behaviour, and future spread of the more transmissible BA.2 subvariant,” modellers warned in their presentation released on Thursday.

COVID-19 Science Advisory Table co-chair Dr. Peter Jüni told CP24 the public should take away a sense of measured caution from this latest projection.

“We don’t pretend the pandemic is over overnight and drop all of the masks like t-shirts on the beach, but just keep transitioning into more liberty over time. (We) slowly increase number of contacts, slowly stop using masks in various situations.”

The Science Table said restrictions on the availability of PCR tests and a lack of positive rapid antigen test results have limited efforts to model the spread of infection in Ontario.

It continues to estimate only one in every 10 infections now makes it into provincial data.

The modellers say the province must be prepared to re-introduce mask mandates, vaccine passports, and continue to improve ventilation and air filtration in public spaces if spread gets out of control.

“The scenarios don’t assume that people change their behaviour like a light switch overnight.”

Ontario Ministry of Health spokesperson Alexandra Hilkene said the province is continuing to focus on maintaining adequate hospital capacity should transmission increase.

"Ontario has done significantly better than the best case scenario provided in the last modelling and we now have the lowest rate of hospitalizations out of all provinces. We have continued to maintain capacity to provide care for all patients who need it, and our hospitals can manage any range in these latest projections.”

THIRD DOSE BLITZ BLUNTED IMPACT OF OMICRON

The modellers also found that the intense campaign to get third COVID-19 vaccine doses to all adults, which started in late December, had a marked impact on hospital admissions caused by COVID-19 the following month.

Without third doses, there would have been more than 5,000 patients admitted to hospital at the peak of Omicron in the third week of January, 34 per cent higher than the observed peak of admissions in the month.

In the ICU, there would have been more than 200 more patients admitted by Jan. 20, a 30 per cent increase over the observed peak in admissions.