If the Virus was already in the USA this portion would not be valid. They cannot alter your policy after a threat already exists whether you know it does or not. If they tried to fight you on it and lost, they would additionally be guilty of bad faith which comes with punitive damages. Some States additionally have a consumer protection act that they would be violating which trebles the damages ( triples )
If this were my policy, I would be seeking a lawyer . California exhumed bodies and proved the virus had been in our Country prior to January 15th that we knew about