Some provinces will begin reopening their economies next week, a move one public health expert described as a delicate experiment — because so little is known about how many people are immune to the COVID-19 virus, or how long such immunity might last.

“This is all going to be tricky,” said Dr. Catherine Hankins, who co-chairs the leadership group of the COVID-19 Immunity Task Force — part of the federal government’s anti-pandemic research strategy.