Nearly 1,000 cases of a new Omicron COVID-19 subvariant dubbed “BA.2.20” have been detected in Ontario since mid-February, and it could have a small growth advantage over the current lineage dominant in the province.

Public Health Ontario says the new subvariant “has been increasingly co-circulating primarily in Ontario and in some American states,” according to a report quietly published on Monday.

A second major iteration of the Omicron variant, known as BA.2, is now dominant in the province as the sixth wave of the pandemic subsides.

This new Ontario-specific subvariant has two mutations that make it different from BA.2, but the exact impact of the mutations is not yet known.

“At this time, the impact of these mutations on transmission, risk of severe disease, reinfection and breakthrough infection is unknown,” Public Health Ontario scientists wrote in their report released earlier this week.

Some 996 cases of the subvariant have been found in the province to date.

An analysis of BA.2.20 cases found to date suggested that there could be up to a 24 per cent growth advantage associated with the new subvariant over the dominant BA.2 strain, but they assessed that finding with a low degree of confidence.

Epidemiologists say the first Ontario case of this new subvariant was detected in London, Ont. on Feb. 14, 2022.

It received a formal Pango lineage designation certifying it as unique back in April.

Its earliest known example worldwide was also found somewhere in Canada in January.

The proportion of BA.2.20 cases has risen in Ontario from less than one per cent in early March to six to seven per cent by mid to late April.

It’s been found most often in Toronto, the wider GTHA and London, primarily among young adults aged 20 to 39.

Eighty-five per cent of known cases involved people who received two or three doses of COVID-19 vaccine.

Only 19 of the 996 examples Public Health Ontario is aware of as of today were detected through border testing of incoming air and land travellers.

Three per cent (30) of the cases identified so far required hospital admission, tracking roughly with observed hospitalization rates of Omicron since March.

No deaths due to infection by BA.2.20 had been observed up until April 20.

As of April, ten per cent of all COVID-19 cases confirmed in Ontario are referred for whole genomic sequencing, down from 50 per cent of all cases detected in March.

New subvariants of COVID-19 strains pop up regularly around the world, but this is the first time such a subvariant has appeared so heavily concentrated in Ontario.

Public health agencies use a lengthy lab-based process known as whole genomic sequencing to map out the unique characteristics of the coronavirus as it evolves, in order to identify the level of risk posed by the changes.