We need much more time to get the data to show how long immunity lasts. The good news that today I read that immunity may last for a least a year. Beyond that period of time, we really don't know as we have not had enough people get immunity for longer than a year. I read an article about a third vaccine may be needed in a year or so.
https://www.cnn.com/2021/05/28/healt...ess/index.html