The Southwest Power Pool, a group of utilities covering 14 states, said the blackouts were "a last resort to preserve the reliability of the electric system as a whole."

The outages forced a Texas county to scramble to administer more than 8,000 doses of Moderna's coronavirus vaccine after a public health facility lost power early Monday and its backup generator also failed, said Rafael Lemaitre, a spokesman for Harris County Judge Lina Hidalgo.

County officials distributed the doses at three hospitals, Rice University and the county jail because those places had large groups of people available where they would not have to drive and with appropriate medical personnel on hand.

"It feels amazing. I'm very grateful," said Harry Golen, a college sophomore who waited for nearly four hours with his friends, much of it in the cold. He was among the last people to get the shots, which otherwise would not have reached students until March or April.

Texas officials said more than 400,000 additional doses due now will not arrive until at least Wednesday because of the storm.