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WASHINGTON (Nexstar) — “I am over 65,” President Joe Biden said, laughing, as he publicly received his COVID-19 booster shot Monday morning.

Biden, 78, rolled up his sleeve for the booster. He’s one of the millions of Americans now eligible for the additional dose of the Pfizer vaccine.

Anyone 65-and-older or with underlying health risks is eligible, along with those in high-risk jobs like first responders, health care workers and grocery store employees — as long as it’s been more than 6 months since their second Pfizer vaccine shot.

But Biden said there’s something more important than booster shots, and that is convincing the unvaccinated to get the initial immunization.

The CDC said 25% of eligible Americans have not received any doses.

“We know that to beat this pandemic and to save lives, to keep our children safe, our schools open, our economy going, we need to get folks vaccinated,” Biden said in remarks before he received the booster.

Unvaccinated Americans put others at risk, the president said. “That’s why I’m moving forward with vaccination requirements wherever I can.”

However, there is still no date for when Biden’s vaccine mandate for employees of large businesses will take effect.

“We knew it would take a little bit of time, given there are some very understandable and good questions by the business community,” White House Press Secretary Jen Psaki said. “We want to ensure there’s clarity when they do put out the rules.”

When it does take effect, Republicans — including a group of 24 state attorneys general — are threatening to sue the administration.