Sadly, this does not sound like an April Fool's Day joke.
ESPN has reported that tonight's Opening Day Game of the Nationals taking on the New York Mets is being postponed due to COVID-19 issues. MLB commissioner Rob Manfred told ESPN that the game is being pushed to tomorrow, April 2.
Yesterday the Nats' general manager, Mike Rizzo, announced that 5 players would not be on the field today due to one of them contracting COVID-19 and the other 4 being in close proximity to him.
According to health and safety protocols put into place by the MLB, "Individuals who test positive will be required to isolate for a minimum of 10 days, receive appropriate care and monitoring from the Club medical staff, and be cleared by the Joint Committee and the individual’s team physician, following a mandatory cardiac evaluation and a determination that the individual no longer presents a risk of infection to others."