On Monday, for the first time in at least 18 months, fully vaccinated visitors from England, Ireland, France, Brazil, China, India, Iran and 26 other previously restricted countries were able to travel to the United States as long as they could show a negative coronavirus test.

And for the first time ever, airlines required proof of vaccination in order to allow thousands of travelers to board flights to the United States.

In terms of travel policy, the change was enormously significant for the United States, signaling a shift toward normalcy welcomed by hotels, restaurants, long-divided families and companies with overseas employees. Photos of emotional airport reunions spread across social media. While travel to the United States from abroad continued to lag when compared to the prepandemic period, it was a busy day.

Customs and Border Protection processed 206,990 international travelers in U.S. airports on Monday. This is nearly 40,000 more travelers than the United States received from abroad on a typical day in 2020. The New York area alone welcomed more than 37,800 people from abroad at Kennedy International and Newark Liberty International airports on Monday, according to the agency. Miami International Airport, the second busiest in the country on Monday, received more than 21,000 travelers from abroad. (Kennedy was the busiest.)

Still, the overall figure of 206,990 passengers, which includes both U.S. citizens and citizens of other countries, lags significantly below prepandemic figures. In 2019, 371,912 air passengers and crew, more than one and half times Monday’s travelers, entered the United States on a typical day. (Estimates for a typical day in 2021 are not yet available and Monday’s figure does not account for crew.)

Numerous airlines are adding flights to their schedules, in the hope that travelers will take advantage of their ability to travel to the United States once again. As of Monday, Air France increased daily flights from Paris to Kennedy to five from three. And British Airways said it increased flights to New York to five from one a day. United Airlines said it was expecting to fly more than 30,000 passengers to the United States on Monday, about 10,000 more than the previous Monday.

But overall, the total number of flights into the United States, 1,376, was not much different than the previous week — up by about 60 flights from the previous Monday, according to Cirium, an aviation data firm.

Numerous airlines and tourism analysts have expressed optimism that the real bump in travel to the United States from abroad will occur over the holidays.