(Reuters) – Many world leaders and senior officials have contracted COVID-19 since the start of the pandemic more than two years ago. Some, such as Canada’s Justin Trudeau and Mexico’s Andres Manuel Lopez Obrado, have caught the virus twice. On Thursday, Joe Biden, 79, the oldest person ever to serve as president of the United States, tested positive. UNITED STATES Former President Donald Trump was 74 when he announced in October 2020 that he had COVID, before vaccines were available and a month before he lost the presidential election to Biden. Trump, who had consistently disregarded guidance…