Natalia Abrahao is lifted by her fiancé, Mark Ogertsehnig, as they greet one another at Newark Liberty International Airport in Newark, N.J., on Monday. Associated Press/Seth Wenig

SAN DIEGO — Parents held children born while they were stuck abroad. Long-separated couples kissed, and grandparents embraced grandchildren who had doubled in age.

The U.S. fully reopened to many vaccinated international travelers Monday, allowing families and friends to reunite for the first time since the coronavirus emerged and offering a boost to the travel industry decimated by the pandemic. The restrictions closed the U.S. to millions of people for 20 months.

Octavio Alvarez and his 14-year-old daughter zipped through a pedestrian crossing in San Diego in less than 15 minutes on their way to visit his mother-in-law in California.

“It’s a big feeling,” said Alvarez, 43, who lives in Ensenada, Mexico, a two-hour drive from San Diego. Prior to the pandemic, his family would visit California twice a month. The emotional cost of the border restrictions were “very high,” he added.

American citizens and permanent residents were always allowed to enter the U.S., but the travel bans grounded tourists, thwarted business travelers and often keep families far apart. Travelers must have proof of vaccination and a negative COVID-19 test.

“I think a lot of people have been waiting for this day,” said Eileen Bigelow, area port director for Vermont for Customs and Border Protection. “They look at it as a light at the end of the tunnel for some return of normalcy.”

There were lots of prolonged hugs at airports from coast to coast. At Newark International Airport in New Jersey, Nirmit Shelat repeatedly embraced his girlfriend, Jolly Dave, after she arrived from India, ending their nine-month separation. She was on the first flight out of the country to the United States.

“I can’t even explain in my words how happy I am,” Dave said.

Gaye Camara, who lives in France, last saw her husband in New York in January 2020, not knowing it would be 21 months before they could hold each other again.

“I’m going to jump into his arms, kiss him, touch him,” said Camara, 40, as she wheeled her luggage through Paris’ Charles de Gaulle airport, where the humming crowds resembled those before the pandemic, except for the face masks.

On the U.S. borders with Mexico and Canada, where traveling back and forth was a way of life before the pandemic, the reopening brought relief. Malls, restaurants and shops in U.S. border towns were devastated by the lack of visitors from Mexico.

San Diego Mayor Todd Gloria, flanked by U.S. and Mexican officials at a celebratory news conference at the San Ysidro crossing, said the economic losses were hefty and the cutting of family ties “immeasurable.”

Retail sales in San Ysidro fell about 75% from pre-COVID levels, forcing nearly 300 businesses to close.

Edith Aguirre of Tijuana took off work to go shopping in San Diego. Bubbling with laughter, she accepted a gift bag from a duty-free store at the San Diego border crossing. She was a regular at SeaWorld in San Diego and last came to the U.S. to celebrate her 50th birthday at Disneyland in February 2020.

“It was very draining,” she said of the interruption to her cross-border life.

Sales dropped in half at David’s Western Wear shop in Nogales, Arizona, which manufactures boots popular among Mexicans.

Owner David Moore hopes his specialty products lure back customers, but he said it won’t happen overnight. Many Mexicans are still trying to get expired visas renewed amid a backlog. Those who do come may be disappointed to find shelves empty because of supply chain problems.

“I really don’t think Mexican shoppers are going to come across in hordes because they have now gotten used to buying a lot of products they need in Mexico,” he said.

David Jerome, president and CEO of the El Paso Chamber of Commerce on Mexico’s border in Texas, said: “It won’t come back as quickly as it was shut off.”

Still, “we feel like we’re getting our neighbors back and we’re glad to get people going back to work,” Jerome said.

Along Canada’s boundary, cross-border hockey rivalries were upended by the travel restrictions. Churches that had members on both sides of the border were suddenly cut off from each other.

But on Monday, border traffic quickly returned.

At Vermont’s busiest international crossing with Canada, U.S. border agents said they began to notice the uptick in border crossing shortly after midnight. By mid-morning, traffic appeared steady.

Travelers at the Peace Bridge in Buffalo, New York, one of the northern border’s busiest crossings, found a 2½-hour wait at 2 a.m., officials said, though within a few hours traffic was flowing more freely. The bridge typically handles about 2 million passenger vehicles from Fort Erie, Ontario, yearly, many of them bound for the region’s shopping malls, ski slopes and sporting events. Volume dropped by more than 90% during the pandemic.

River Robinson’s American partner wasn’t able to be in Canada for the birth of their baby boy 17 months ago. She was thrilled to hear about the U.S. reopening and planned to take the child to the U.S. for Thanksgiving.

It’s “crazy to think he has a whole other side of the family he hasn’t even met yet,” said Robinson, who lives in St. Thomas, Ontario.

Airlines are preparing for a surge in activity — especially from Europe — after the pandemic and resulting restrictions caused international travel to plunge.

The 28 European countries that were barred made up 37% of overseas visitors in 2019, according to the U.S. Travel Association. As the reopening takes effect, carriers are increasing flights between the United Kingdom and the U.S. by 21% this month over last month, according to data from travel and analytics firm Cirium.

In a sign of the huge importance of trans-Atlantic travel for airlines, British Airways and Virgin Atlantic celebrated the reopening by synchronizing the departures of their early morning flights to New York on parallel runways at London’s Heathrow Airport.

Maria Giribet, 74, who lives on the Mediterranean isle of Majorca, was headed to San Francisco where she planned to “suffocate” her twin grandchildren with hugs after missing half their lives. Gabriel and David are now 3½.

The U.S. will accept travelers who have been fully vaccinated with any of the shots approved for emergency use by the World Health Organization, not just those in use in the U.S. That’s a relief for many in Canada, where the AstraZeneca vaccine is widely used.

But millions of people around the world who were vaccinated with Russia’s Sputnik V, China’s CanSino or other shots not approved by the WHO will not be able to travel to the U.S.

Testing and quarantine requirements remained obstacles for others. A mobile testing truck was parked near the Peace Bridge in New York, promising results in 30 minutes for $225 and next-day results for $160.

Marcela Picone, 39, of the Buffalo suburb of Williamsville, has been waiting for the day her fiancé and father of her 2- and 3-year-old children can visit from Stoney Creek, Ontario. But his 15-year-old son would have to miss school to quarantine upon their return if they traveled.

“He’s a dad to two American kids,” she said. “He should have had the right to come into this country the entire 19 months.”