But of course. That’s how viruses works. They burn out pretty quickly, if allowed to go through a population.
Then, a mutation, that is weaker but spread more fiercely, take over. Hence, new flu vaccines are developed each year. Hence, new covid boosters are touted. It’s an attempt to keep up with mutations.
Lock a population up and the virus will have more time to mutate, instead of burning out. The casualties will possibly be the same, but drawn out over a longer period.