More than 300 million COVID-19 vaccine doses have now been administered in the U.S., the Centers for Disease Control and Prevention confirmed Sunday.

Why it matters: The latest CDC figures show that 41.9% of the U.S. population has been fully vaccinated against the coronavirus and 51.5% has received at least one dose.

• The vaccination milestone comes as the U.S. has seen new infections fall to the lowest level since March 2020, when the pandemic began.

By the numbers: As of Sunday, 301,638,578 COVID-19 doses have been administered across the U.S., according to the CDC.

• The seven-day average of new daily infections reported has dropped from 65,053 on April 1 to 12,780 as of June 5, per the CDC reported.
• The seven-day average of new deaths from the coronavirus confirmed in a single day has fallen from 681 to 367 during the same period.

Yes, but: The vaccination rate has slowed down to just over 1 million COVID-19 doses per day after a high of 3.3 million a day in April, according to CDC statistics.

• That's despite anyone over the age of 12 being eligible for a dose since last month.

What to watch: NIAID director Anthony Fauci warned Friday that vaccine complacency could lead to another surge, "particularly with variants floating around," and "that could set us back to the time when we had to shut down things, CNN reports.

Go deeper: Why Biden's latest vaccine goal is his hardest yet

Editor's note: This article has been updated to reflect the vaccine rollout slowdown.