USA is having an unusual "double-barreled" flu this year where two different variants are common. One of which is A/H1N1 appeared as a second wave late in the

USA is having an unusual "double-barreled" flu this year where two different variants are common. One of which is A/H1N1 appeared as a second wave late in the flu season. Not sure what coronavirus will do, but clearly diseases like H1N1 can recur. What is somewhat more scary is that particularly lethal diseases often get less aggressive over time because the less aggressive variants transmit better and offer protection against the more aggressive variants. But since coronavirus can spread before symptoms appear, it's not clear that the same feedback loop will occur.