Preliminary data released months ago suggested a significant decline in the vaccines’ effectiveness at preventing infection, although they held up well against severe disease.

Based on that data, the Biden administration had hoped to begin allowing booster shots in September for any American adult who was at least eight months removed from their second dose.

The CDC and the FDA opted instead to only authorize boosters for seniors, people with high-risk medical conditions and people at high risk of infection, before opening them last week to everyone at least six months out from their initial shots.

In the meantime, red and blue states alike decided to ignore the CDC and open up booster eligibility on their own, and breakthrough infections have become increasingly common.