Northern states are becoming American COVID-19 hotspots as winter weather returns

Just past the border, right on Canada's doorstep, the United States is witnessing the return of a miserable and now-familiar fact of life in a pandemic entering its third winter.

Cases are surging in northern states — to record levels in some areas — as America's hottest COVID-19 hotspots are once again places with the coldest winters.

The annual human retreat to indoor spaces has abetted transmission in places like Michigan, Minnesota and Vermont —and created new dilemmas for Canadians.

At least one municipal body is now cautioning against cross-border trips.

The public-health authority of Thunder Bay, Ont., has urged against non-essential travel to Minnesota, Wisconsin and Michigan where case rates are much higher than Canada's.

"They're at least 10 times [higher in Minnesota than] our rates here," Dr. Janet DeMille,  Thunder Bay's medical officer of health, told CBC News.

"You could very easily bring it back to our area. … Consider not doing that travel at this time." 

DeMille blamed a few factors for the delta wave gaining strength: the winter weather, school re-openings, increased travel and the looser pandemic practices in the U.S. (including lower vaccination rates). 

"[It's] getting colder. It's getting darker. We're not out so much. Maybe we're getting together more in indoor spaces," she said. "All this contributes to the spread of the virus."

It could also contribute to a post-holiday surge in Canada, she said.

There's a pattern in the current pandemic case spread that shows cases rising as temperatures drop — increasing the further north you travel, as more people head indoors to stay warm.  

That's a geographic change from summer months, when southern states suffered a pandemic pounding as people went into air-conditioned places to escape the heat.

If you were to head up the Eastern Seaboard of the United States now,  the further north you moved, the faster you'd see cases rising.