US President Joe Biden has received an updated Covid-19 booster shot. “This virus is constantly changing,” Biden said on Tuesday afternoon at the Eisenhower Executive Office Building near the White House. “New variants have emerged here in the US and around the world. Your old vaccine or your previous Covid infection will not give you maximum protection,” he warned. More than 20 million Americans have received updated Covid-19 vaccine so far, Xinhua news agency reported, citing the White House.The US has reported 97 million Covid-19 cases, along with more than 1 million deaths, according to data from Johns Hopkins University.