OCEAN ISLE BEACH, N.C.—A winter storm that left millions without power in record-breaking cold weather claimed more lives Tuesday, including three people found dead after a tornado hit a seaside town in North Carolina and four family members who perished in a Houston-area house fire while using a fireplace to stay warm. The storm that overwhelmed power grids and immobilized the Southern Plains carried heavy snow and freezing rain into New England and the Deep South and left behind painfully low temperatures. Wind-chill warnings extended from Canada into Mexico. In all, at least 16 deaths were reported. Other causes included car crashes and carbon monoxide poisoning. The weather also threatened to affect the nation’s COVID-19 vaccination effort. President Joe Biden’s administration said delays in vaccine shipments and deliveries were likely. North Carolina’s Brunswick County had little notice of the dangerous weather, and a tornado warning was not issued until the …