Evidence for vaccine booster shots isn't clear, but Biden moves ahead anyway

The U.S. is poised to begin rolling out booster shots in a matter of weeks, with still one major sticking point to resolve: It's not entirely clear yet that third shots are needed.

President Joe Biden recently vowed to begin deploying boosters the week of Sept. 20, pending a green light from federal regulators.

But health experts advising the government on that decision say the August announcement by Biden's political appointees came as somewhat of a surprise. It also was unclear, they said, why that date was chosen at all.

Evidence for boosters is still mixed, and announcing a...