So far, the toughest responses to the rise of the variant—which was only declared a “variant of concern” by the WHO on Friday—have tended toward barriers to entry, as Japan and Israel announced in recent days.

Some countries have started to tighten internal measures, too: In the United Kingdom, Prime Minister Boris Johnson has announced travel restrictions, and also said that mask requirements—previously dropped in England—would be reintroduced to try to halt the spread of the virus.

Here are a partial list of countries that have introduced new Omicron-related restrictions in recent days:

• The U.S. will restrict travel from South Africa and seven other southern African countries.
• The European Union, meanwhile, has enacted similarly targeted measures aimed at southern Africa.
• The Japanese government announced on Monday that the country’s borders will be closed as of Tuesday to all foreigners, including business travelers and international students.
• After reopening its borders to vaccinated tourists four weeks ago, Israel announced another blanket ban over the weekend.
• Morocco instituted a similar ban, which goes into effect on Monday.
• Indonesia is barring travel to and from Hong Kong and southern Africa.
• Australia will delay by two weeks its plans to open its borders to those coming from Japan and South Korea, including tourists, students, and skilled migrants.

Ineffective and discriminatory

Many experts, as well as people in the countries affected, feel that travel bans are ineffective, however, pointing out that the variant has already spread widely.

On Sunday, South African President Cyril Ramaphosa called the travel bans discriminatory, and said they would not stop the virus from spreading. “The only thing the prohibition on travel will do is to further damage the economies of the affected countries and undermine their ability to respond to, and recover from, the pandemic,” he said, according to the BBC.

Many scientists agree.

“Porous travel bans will do very little to slow the spread of an airborne virus…the U.S. & world should be getting vaccine & resources to vaccinate people across Africa,” tweeted Rick Bright, the immunologist who is CEO of the Rockefeller Foundation. “Nationalism & token donations will not end a global pandemic, it risks making it much worse.”

“It makes zero sense to impose stricter border control measures unless countries are also willing to very strictly ramp up their domestic public health measures,” Karen Grépin, Associate Professor at the school of public health at the University of Hong Kong, told Fortune.

“If countries really do want to prevent this from taking route and spreading wildly, then it can’t be just about the border,” she said.

Experts have pointed toward the inequality at the heart of the vaccine rollout. They warn that a lack of vaccine access in less wealthy countries would simply accelerate new virus mutations, ultimately threatening how effective those vaccines will be.

There are also plenty of unanswered questions about the variant, with health experts cautioning that we still don’t know exactly how dangerous the new variant is. Dr. Angelique Coetzee, chair of the South African Medical Association, told Reuters over the weekend that the Omicron cases she had seen were mild and that patients recovered quickly.

There are other reasons to hope the restrictions will be temporary. Countries are desperate not to lose another Christmas after memories of canceled holidays last year remain fresh: from unopened Christmas markets in Berlin to lockdowns last year in South Africa. Already, economists are slashing their growth forecasts to account for Omicron-related shutdowns and travel bans.

Additional reporting from Eamon Barrett