Finally, is the question of how long a vaccine will last.
In some instances, your immune system can have a very long memory.
"Some natural infections can give you lifelong immunity," [Stephen] Jameson says. "You only get it once, and you're protected for the rest of your life."
Vaccines mimic a natural infection to trigger an immune response. But vaccines may require a boost to keep that immunity strong. The memory B cells that target the coronavirus that causes COVID-19 may not have the staying power of the cells that protect us from the measles, for instance. So far, scientists have observed that these memory B cells have persisted for many months following a case of COVID-19, but it's too early to say anything about whether they will eventually fade.
"The good thing is there would be the opportunity that if it turned out there was some waning of the immune response," Jameson says, "then, like many other vaccines, maybe ... you get another booster after a year or something."
These questions reflect how much scientists have come to understand about our immune system in recent years. COVID-19 is also illuminating what we still don't know about how the immune system defends us from infectious germs....