TORONTO — The sometimes double-digit warm winter weather may be partly responsible for a mild flu season so far this year, but influenza cases are now on the uptick and Ontario is not out of the woods yet, a top public health official says.
Figures released Friday by Public Health Ontario show 3,401 confirmed influenza cases and 12 deaths at this point in the 2015-16 flu season. Those numbers are a fraction of the numbers from the 10,000 cases and 211 deaths the same time last year.
The 2014-15 flu season was a nasty one due to the prevalence of the potent H3N2 strain, which wasn’t effectively countered by vaccines.
Dr. Doug Sider with the health agency said one reason for the milder hit this season is the less difficult strains going around.
“This year is going to have to be better than that because there is less H3N2 and less H1N1 activity,” said Sider, director of communicable disease prevention and control.
Cases in the traditionally peak months of December-January are nearly non-existent, but started taking off as 2016 set in — which came as a surprise to Sider in his 24-odd years in public health.
“I’ve never seen that type of a December-January,” he said.
“It’s a very late season. And it’s a very late season that’s got predominately pandemic H1N1 and influenza B,” Sider added.
But Sider said that while those earlier winter months were relatively free from the flu, viruses with similar symptoms — such as coronavirus — stepped in.
“A whole bunch of other respiratory viruses in a way sort of filled the space that was vacated earlier in the winter.”
Why? It just might be due to the warm weather, he said.
“Could that have been the case? Possibly. But we really don’t understand all the factors that go into the seasonality of influenza,” he said.
“Some of it has to do with cold weather, immune system issues, crowding and close personal contact in the winter months, sunshine immune system weaknesses… we really don’t have a good handle on it.”
Sider said another unique feature of the current flu season is that the majority of influenza A cases (accounting for virtually all flu cases) are affecting not seniors but rather those in the healthy prime of their life — aged 20 to 64.
The doctor said this may be due to the fact that younger people have less natural immunity to the dominant strain.
“So they’ve got some sort of a residual immunity to the pandemic H1N1 strain versus people in their 20s, 30s, 40s, etc., who have less exposure over the years.”
Public Health Ontario says flu shots remain available and that there’s still benefit from getting one now.
With a file from Allison Vuchnich