What is the current data/thinking saying about longevity of vaccine efficacy against severe disease? If that…

What is the current data/thinking saying about longevity of vaccine efficacy against severe disease? If that does fall off a cliff too, does it mean those with vaccine-only immunity are at increasing risk of severe disease? @ejustin46? @DavidJoffe64 ? https://t.co/mnel1JyArn