In some people, antibodies start to wane at that point, but they still have antibodies for some time. So there’s definitely at least some immunity for longer than that, plus other types of immunity (T-cell, etc.) Plus, if everyone is losing immunity over different time frames, they’re not going to contract it nearly as easily as when we were all at zero, since many others around them will still be immune. The staggering probably helps a lot. I think the same is true for colds, and I don’t get a cold every couple of months, though I know some people do. More like once a year, and colds are caused by a bunch of different viruses, so it’s not even once a year for each virus.
In some people, antibodies start to wane at that point, but they still have antibodies for some time. So there’s definitely at least some immunity for longer than that, plus other types of immunity (T-cell, etc.) Plus, if everyone is losing immunity over different time frames, they’re not going to contract it nearly as easily as when we were all at zero, since many others around them will still be immune. The staggering probably helps a lot. I think the same is true for colds, and I don’t get a cold every couple of months, though I know some people do. More like once a year, and colds are caused by a bunch of different viruses, so it’s not even once a year for each virus.