another factor.. They are not sure how long covid immunity might last for people.
We still don’t know what COVID-19 immunity means or how long it lasts | Science News
[Two new studies demonstrate how severity of disease is predictive of longer-lasting antibody production and detail how immunity wanes over time but may exist for up to 7 months.]
Studies show long-term COVID-19 immune response | CIDRAP
Coronavirus Disease 2019 (COVID-19) | CDC
CDC COVID Data Tracker