When will we need COVID boosters?

How will we know if we need COVID vaccine boosters?
If we observe that:
(1) Vaccine protection wanes over time.
(2) New immune escape variants emerge, resulting in a vaccine-strain mismatch.
These are distinct reasons. We can imagine how we would distinguish these in the data.

— Natalie E. Dean, PhD (@nataliexdean) May 27, 2021