The campaign to vanquish the coronavirus is picking up speed. Britain has begun dispensing the second vaccine in its arsenal. And India, the world’s second-most populous country, has authorized its first shots. In the U.S., meanwhile, government officials say that the pace of vaccinations has accelerated markedly after a disappointingly slow start. Dr. Anthony Fauci, the nation’s top infectious-disease expert, said over the weekend that 1.5 million shots were dispensed over 72 hours, bringing the running total to about 4 million.