For months, air travel has rebounded steadily and Sunday was the busiest travel day at U.S. airports since February 2020. But the discovery of the Omicron coronavirus variant threatens to derail the industry’s recovery, as did the Delta variant this summer.

Several countries, including the United States, have banned visitors from South Africa and a handful of neighboring countries. Japan, Morocco and Israel have banned all incoming foreign visitors, while the Philippines has banned visitors from southern Africa and several European countries.

The tightening of restrictions has drawn criticism from the travel industry. In a statement last week, Willie Walsh, president of the International Air Transport Association, a global trade association, called for “safe alternatives to border closures and quarantine.” Over the weekend, the US Travel Association urged the Biden administration to rethink its ban.

“The Covid variants are concerning, but the border closures have not prevented their presence in the United States as vaccinations have been shown to be incredibly durable,” said Tori Emerson Barnes, executive vice president of public affairs and health. policies, in a press release. “With a vaccine and testing required to enter the United States, we continue to believe that assessing an individual’s risk and health status is the best way to welcome qualified international travelers to the United States. United. “

For US airlines, the rebound in international travel has been slower than that in travel within the United States. But President Biden’s move to ease long-standing restrictions on foreign travelers this month promised to spur that recovery. It is not yet clear whether or how the Omicron variant will affect travel demand, but if travel bans proliferate and concerns about the variant continue to spread, hopes of an accelerated international rebound may be dashed again.

Only two American carriers, Delta Air Lines and United Airlines, leave southern Africa. The two said they did not yet plan to adjust their schedules in response to the administration’s ban, which went into effect on Monday and does not apply to U.S. citizens or lawful permanent residents. Delta operates three weekly flights between Atlanta and Johannesburg. United operates five flights a week between Newark and Johannesburg, and did not change plans to restart flights between Newark and Cape Town on Wednesday.

No major US airline has announced substantial procedural changes due to the variant. And all passengers flying to the United States must provide proof of a negative coronavirus test, with non-citizens also required to be fully vaccinated.

In the United States, air travel has almost recovered, although many companies are still reluctant to send employees on business trips. The number of people screened at airport security checkpoints over the past week fell only 12% from the same week in 2019, according to the Transportation Security Administration.

The industry easily handled the crush of travelers over the holiday week, avoiding the disruption that has lasted for days at some airlines in recent months. In the seven days ending Sunday, there were fewer than 600 cancellations, representing less than 0.5% of all scheduled domestic flights, according to FlightAware, an aviation data provider.