ABC News Live: 21,600 people evacuated from Afghanistan in past 24 hours.

Plus, New York City public schools mandate vaccines for all teachers after FDA approval of the Pfizer shot.

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Homeland security calls footage of agents on horseback 'extremely troubling'.

Homeland security calls footage of agents on horseback 'extremely troubling'.

At least 10,000 migrants, mostly from Haiti, are still camped out near the Del Rio International Bridge.

Johnson & Johnson: Booster shot could boost immunity.

Johnson & Johnson: Booster shot could boost immunity.

New data shows that two shots given two months apart resulted in 94% protection against symptomatic disease.

Biden addresses United Nations General Assembly - ABC News.

Biden addresses United Nations General Assembly - ABC News.

President Joe Biden spoke at the U.N. General Assembly for the first time as president, addressing U.S. diplomacy amid tensions with allies. SUBSCRIBE to ABC News on YouTube: Latest updates: Watch FULL EPISODES on Hulu: #ABCNews #UNGA #Biden

Dow plummets in biggest 1-day drop in months

Dow plummets in biggest 1-day drop in months

ABC News chief business correspondent Rebecca Jarvis reports on what set off a stock market plunge on Wall Street on Monday.

Images show border patrol agents attempting to push back migrants.

Images show border patrol agents attempting to push back migrants.

The U.S. Department of Homeland Security has called new footage of border patrol agents on horseback attempting to push back migrants as they cross the Rio Grande "extremely troubling."