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In its weekly e-newsletter to doctors on Friday, the public health unit says the number of flu cases is rising in Toronto and Ontario.

It says flu activity is likely to peak at the end of December or early January and asks health-care providers to move quickly to provide the shot to unvaccinated patients, especially those at high risk of severe illness. 

The dominant strain circulating right now, called H3N2, has mutated since the flu vaccine was developed several months ago.

The public health unit is asking health-care providers to remind patients that the vaccine can still help prevent severe illness and hospitalization even if it's not a perfect match.  

Preliminary data from the U.K. suggests that in the early days of its flu season this year, the shot provided 72 to 75 per cent protection against emergency department visits and hospitalizations for kids and adolescents between two and 17 years old. 

That data showed 32 to 39 per cent effectiveness in protecting adults from those visits. 

Older adults are at especially high risk of getting severely ill from the flu and doctors strongly recommend they get vaccinated. 

Public Health Agency of Canada data shows flu cases started rising sharply in November. 

This report by ¹ú²úÓÕ»ó¸£Àû was first published Dec. 5, 2025.

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