Barack Obama has tested positive for a mild case of Covid-19, the former US president said on his Twitter account Sunday. “I’ve had a scratchy throat for a couple days, but am feeling fine otherwise,” Obama tweeted, adding that his wife, former first lady Michelle Obama, has so far tested negative. “Michelle and I are grateful to be vaccinated and boosted,” he wrote. Obama, plus fellow former presidents Jimmy Carter, George W. Bush, Bill Clinton – and the former first ladies – appeared together in a one-minute video released last March, endorsing the US vaccination campaign and sharing what th…