Why it matters: Two doses of Pfizer and Moderna’s vaccines — or one dose of J&J — aren’t very protective against Omicron infection, according to preliminary data, although they likely work much better against severe disease.

But some experts warn that giving a booster shot too soon could diminish its effects.

Where it stands: Anyone 16 and older who got their second Pfizer or Moderna shot at least six months ago is eligible for a booster shot in the U.S., as are people who received a J&J shot at least two months ago.

But 58 million Americans received their second shots within the last six months, per CDC data.