TORONTO—New cases of COVID-19 infections across Canada are trending upward, public health authorities reported on Wednesday, amid new concerns over vaccine supplies. Thousands of new cases on average and 31 deaths were being reported daily, the Public Health Agency of Canada said in its latest update. The bottom line, the agency said, was that people still face a serious risk of contracting the disease. “Amid increasing case counts, shifting severity trends, and a rising proportion of cases involving variants of concern in heavily impacted areas of Canada, we need to remain vigilant,” Dr. Theresa Tam, the country’s top public health officer, said in a statement. “Maintaining public health measures and individual precautions is crucial to reducing infection rates and avoiding further spread of new variants.” While vaccinations offer some hope for containing the pandemic, concerns about supplies were rekindled after India put a halt to exports of its Oxford-AstraZeneca vaccine …