Some provinces hit hard by the third wave of the COVID-19 pandemic have moved toward shedding more public health restrictions, but a national group is calling for those governments to slow their plans.

Zero COVID Canada sent a letter Thursday to the premiers of British Columbia, Alberta, Saskatchewan, Manitoba, Ontario and Quebec "to express our deepest concerns regarding the reopening plans."

"As more and more evidence comes in, it appears that a single dose of the vaccine — including Pfizer — is only about 30 per cent effective against the Delta variant, which is ravaging India and the U.K. right now," the letter says.

"Each new variant has the potential to evade vaccination efforts, and we need to protect our efforts to date."

The group is made up of researchers, physicians, engineers, activists, lawyers, educators, and concerned citizens.

It noted that the variant first identified in India has already caused multiple outbreaks in Canada, including at the Foothills Medical Centre in Calgary, and is behind case spikes in Manitoba and in Peel Region outside Toronto.

Zero COVID Canada also recommends that provinces keep masking and physical distancing, and to only restore capacity limits indoors when 70 per cent of residents are fully vaccinated.