coronavirus. Health Canada adding AstraZeneca blood clot warning, but says vaccine is safe In a series of tweets on Tuesday, Canada’s top doctor Theresa Tam said as vaccine delivery begins to “ramp up at an accelerated pace,” there are “hopeful signs for better days ahead.”“However, the #VariantsOfConcern trend is cause for continued caution,” she wrote.“Amid increasing case counts and shifting severity trends, a rising proportion of cases involving #VariantsOfConcern means we need to remain vigilant, maintaining public health measures and individual precautions.”2/2 Amid increasing case counts and shifting severity trends, a rising proportion of cases involving #VariantsOfConcern means we need to remain vigilant, maintaining public.