Biden, 78, meets guidelines issued last week by the Food and Drug Administration and the Centers for Disease Control and Prevention that those over age 65 get a third vaccination. 

The president received his first shot in December and his second in January, putting him well past the six-month threshold for receiving a third shot. 

Biden is touting booster shots as many countries are struggling to get enough supplies to provide initial doses. Some public-health advocates say vaccines should be shipped to countries without adequate supplies before the U.S. gives third shots.

The U.S. is starting to lag behind some other countries in the percentage of its population that’s been fully vaccinated, as a portion of its population continues to resist getting shots. 

Just over 55% of the U.S. is fully vaccinated, according to the Bloomberg vaccine tracker. The United Kingdom is at 67% fully vaccinated and Canada is at 70.6%, while Portugal, at 83.7%, has the highest percentage of the fully vaccinated among countries with populations of more than 1 million.

Biden had suggested in August that he hoped every American who was fully vaccinated would be able to get a booster dose several months after their previous shots. But the Food and Drug Administration and Centers for Disease Control and Prevention offered narrower recommendations last week. 

CDC Director Rochelle Walensky approved boosters for those over 65 and those 18 to 64 with underlying conditions. She overruled an advisory panel to approve boosters for 18-to 64-year-olds who face high risks of exposure in their workplaces.

The groups that are initially eligible for the booster are also the ones that also had the earliest access to the previous rounds of Pfizer shots, making them likelier to be clear of the six-month window since their second shot. There are signs that the efficacy of the initial two-shot regimen of the Pfizer-BioNTech vaccinate is waning over time, particularly for the elderly, and that they’re not as effective against the Delta variant as they were against earlier strains.

Boosters of the Moderna Inc. and Johnson & Johnson vaccines haven’t yet been approved by U.S. regulators.

—With assistance from Josh Wingrove.

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