\u201cA concerning rise in flu cases at CHEO has led to a significant increase in the number of children coming to the Emergency Department since the start of cold and flu season, with many children needing hospitalization with the flu,\u201d the statement read.<\/p>\n
During those peak months, 40.5 per cent of people who tested for the flu were positive, a rate four percentage points higher than the Ontario average, according to Ottawa Public Health.<\/p>\n
Data from OPH also showed Ottawa recorded a decade-high 257.9 confirmed cases of Influenza A and B per 100,000 people, more than either Toronto or Ontario.<\/p>\n<\/p>\n
Earl Brown, an expert in influenza virulence at the University of Ottawa, said the spike in flu cases was due to a mutated strand of the H3N2 subtype and waning vaccination rates. The H3N2 subtype has been dormant since 2022-23, but made landfall again this year.<\/p>\n
Brown said this year\u2019s new \u201csubclade K variant\u201d of the H3N2 strand had an abnormal number of mutations and was a vaccine mismatch.<\/p>\n
\u201cIn normal years you\u2019ll get about one to three (mutations). Five is usually considered a lot. And this one had seven,\u201d Brown said. \u201cThis year, there was less protection because the virus had changed more.\u201d<\/p>\n
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Dr. Earl Brown, University of Ottawa<\/p>\n
This year\u2019s vaccine was 40-per-cent effective at fending off the new variant \u2014 a surprise, Brown said, considering the increase in the number of cases.<\/p>\n
Forty-six per cent of Ottawa\u2019s residents aged 18 and older received the vaccine in 2024-25, with an even lower uptake of 37 per cent of those aged 17 and younger, according to data provided by OPH.<\/p>\n
Brown said all these factors \u2014 a new, mutated strand and low vaccination rates \u2014 created a perfect storm for an influenza surge.<\/p>\n
\u201cSo along you come with a new virus that can overcome pre-existing immunity. Immunity was already poor because of lack of vaccination,\u201d Brown said. \u201cAnd we\u2019ve got a very record-breaking year of influenza.\u201d<\/p>\n
He added that Ottawa likely had a higher rate of positive tests than Toronto and Ontario this year because of the city\u2019s older demographic.<\/p>\n<\/p>\n