President Joe Biden on Friday urged those now eligible for boosters of Pfizer's COVID-19 vaccine to get the added protection a day after the Centers for Disease Control and Prevention endorsed the extra doses for millions of older or otherwise vulnerable Americans. 

Now public health officials must clear up confusion over exactly who should get a booster, and why — as they juggle vaccinating the unvaccinated who still make up the vast majority of the nation's coronavirus cases.

People 65 and older, nursing home residents and those ages 50 and up who have chronic health problems such as diabetes should be offered a booster once they're six months past their last Pfizer dose, CDC Director Dr. Rochelle Walensky ruled late Thursday.

And a broad swath of other adults can decide for themselves if they want a booster once they reach that six-month mark: Younger people with underlying health problems — plus people at increased risk of infection because of their jobs, such as health workers, or their living conditions, such as jails or homeless shelters.

Walensky overruled objections from her own advisory panel in adding that last category, but the decision drew praise from health organizations that need their employees to avoid even a mild infection so they can come to work.

"At a time when hospitals across the country are experiencing ongoing surges in COVID-19 hospitalizations and severe workforce shortages, all available tools — including booster shots — should be considered to keep frontline health care workers safe and safeguard access to care," said American Hospital Association CEO Rick Pollack.

The booster decision comes even as CDC data shows the vaccines used in the U.S. still strongly protect against severe illness, hospitalizations and death from COVID-19, although immunity against milder infection appears to be waning somewhat months after getting the shots.

"You're in good shape and we're doing everything we can to keep it that way, which is where the booster comes in," Biden said Friday as he praised the decision. He aimed to set aside any unease about another vaccination by saying he would get his own booster soon.

"It's hard to acknowledge I'm over 65, but I'll be getting my booster shot," Biden said. "It's a bear, isn't it?" 

The approval prompted many Americans to immediately seek their own boosters.

Jen Peck, 52, of Eau Claire, Wisconsin, got the booster first thing Friday morning. She qualified as a math and science consultant at rural schools in Wisconsin, and got her last Pfizer dose in March.

"It's a little scary out there," she said of her job traveling between school districts in places where many students and teachers don't wear masks and the younger children aren't vaccinated.

"Because I go from building to building I don't want to be COVID Mary carrying it around to buildings full of unvaccinated kiddos. I could not live with myself if I carried it from one building to another. That haunts me, the thought of that," Peck said.

CDC's Walensky said getting the unvaccinated their first shots remains the top priority. But her advisers on Thursday wrestled with whether the booster debate was distracting from that goal, especially if the shots were opened to the wide swath of Americans that Walensky ultimately settled on.

Only about 182 million Americans are fully vaccinated, or just 55% of the population.

It's rare for a CDC director to overrule the panel recommendation; experts said it has only happened once this century.

Still to come: Government decisions on whether to allow booster doses of vaccines made by Moderna and Johnson & Johnson.

Britain and Israel are already giving a third round of shots over strong objections from the World Health Organization that poor countries don't have enough for their initial doses.

The U.S. had already authorized third doses of the Pfizer and Moderna vaccines for certain people with weakened immune systems, such as cancer patients and transplant recipients. Other Americans, healthy or not, have managed to get boosters, in some cases simply by asking.