They're talking about the strong possibility that the virus has begun mutating again in the UK, and even the probability that it have already done so in the US and we just don't know it. . . .
But, I believe it was MWoO who said it's impossible for the virus to mutate, and since he apparently knows everything and we never know what we're talking about, I guess this means it's all just fake news, and there's really nothing for us to worry about.