Recently, the news reported that some of the healed person tested negative who did properly did protection but when they go test again they got positive and some of them does not show a symtom(may be not yet) and the news said that they can infect others.
My question 1: when a person's body successfully fought the virus, their body will got the antibody, then what caused the positive when they tested second time? the antibody not strong enough? the virus mutated? or the 1st time test after healed was a false negative?
Question2:when an infected person does not show a symtom can they really infect others?