Governments around the world — including those of the United States, Britain and New Zealand — are moving to impose stricter travel limitations in a bid to slow the spread of new coronavirus variants that experts warn are more contagious.

President Biden confirmed Monday that he would extend a ban on travelers from Brazil, the United Kingdom, Ireland and 26 other European countries. Visitors from South Africa will be banned from entering the United States starting Saturday.

New Zealand, which has been lauded for its handling of the pandemic, may keep its borders closed to visitors for “much of this year,” Prime Minister Jacinda Ardern said.

Here are some significant developments:

The new U.S. restrictions come as several countries reconsider eased travel polices amid worry over virus variants that can make people sicker, spread faster and, in some cases, compromise the effectiveness of vaccines.

“With the pandemic worsening and more contagious variants spreading, this isn’t the time to be lifting restrictions on international travel,” White House spokeswoman Jen Psaki said during a news briefing Monday.

Total cases in the United States top nearly 25.3 million and death tolls are inching toward 422,000 since the start of the pandemic, according to Washington Post data.

The new travel policy is better than restrictions posed under former president Donald Trump because the list of countries is more expansive and testing is a factor, but it’s still “less than excellent,” Tom Russo, professor and chief of infectious disease at the University at Buffalo Jacobs School of Medicine and Biomedical Sciences, said in an interview.

Testing is imperfect and much of the quarantining still relies on an honor system instead of a controlled site, as countries such as New Zealand and Australia have done, he said.

“This travel ban is helpful in that it’ll decrease the likelihood of variants entering the country, but it’s leaky,” Russo said, adding that the exception for family members to enter could be trouble. “This is better than nothing, but it’s not the most rigorous policy. It’s a middle-of-the road policy.”

Countries that have been more stringent about who they allow to cross their borders are now trying to cope with a new variant.

Australia suspended its travel bubble with New Zealand on Monday for at least three days after a woman in Auckland was determined to have contracted the South African coronavirus variant. The woman had been in quarantine at an Auckland hotel, where officials think she may have contracted the virus from another quarantining person.

New Zealand’s prime minister said Tuesday that the country’s borders would probably stay closed to foreign visitors for the duration of the year, citing concerns about the global vaccination rollout.

“The rest of the world simply poses too great a risk to our health and our economy to take a risk at this stage,” Ardern said at a news conference in Wellington.

Britain, meanwhile, is set to announce Tuesday whether it will channel some new arrivals into quarantine hotels as it runs a high-stakes, real-world vaccine experiment in a bid to extend the time between doses to stretch its reserve.

The country also announced Tuesday that it will lend its genomic expertise and capacity in tracking new variants of the SARS-CoV-2 virus, which causes covid-19. The program, called the New Variant Assessment Platform, will help other countries identify changes in the virus while giving early warnings of new mutations that could be a threat to Britain.

Health Secretary Matt Hancock said in a statement that the pandemic has shown the importance of maintaining not only the health of Britons and their neighbors, “but the health of people across the world.”

“Our New Variant Assessment Platform will help us better understand this virus and how it spreads and will also boost global capacity to understand coronavirus so we’re all better prepared for whatever lies ahead,” he said.

The push to help other countries combat the virus and its variants comes in the wake of Washington Post reporting that only one of 29 of the world’s poorest countries has started coronavirus vaccinations. The startling revelation has health experts worried, as further spread of the virus can leave room for more variants to emerge, which could render vaccines less effective.

Despite fears about vaccine rollouts in some countries, the International Monetary Fund is projecting growth for the global economy in 2021.

The financial institution’s revised 2021 forecast is driven by hopes of coronavirus vaccinations, it said in its most recent World Economic Outlook.

In the January update, the organization projects that the global economy will grow 5.5 percent in 2021 — up 0.3 percentage point from October, credited to “expectations of a vaccine-powered strengthening of activity later in the year” — and 4.2 percent in 2022. For the United States, the IMF projects growth in 2021 of 5.1 percent and 2.5 percent for 2022.

That expectation of recovery comes after a pandemic-induced collapse of the global economy during 2020, which the IMF listed as disproportionately affecting women, youths, impoverished people and contract and temporary workers. The update expects global growth contraction in 2020 to have dipped 3.5 percent, nearly 1 percentage point higher than what October’s forecast projected, thanks to stronger-than-expected momentum in the second half of the year.

“Although recent vaccine approvals have raised hopes of a turnaround in the pandemic later this year, renewed waves and new variants of the virus pose concerns for the outlook,” the report reads.

As the vaccines bring hope of financial growth, countries across the globe are still monitoring how to best control the spread of covid-19 and its emerging variants.

The European Union proposed a new round of travel restrictions Monday.

Ursula von der Leyen, president of the European Commission, said in a Twitter post that new variants spreading across member nations have influenced the new round of restrictions.

“We need to keep safe & discourage non-essential travel,” she wrote. “ … In parallel, we propose stronger requirements for international travellers into the EU: testing, quarantines and a future common European Passenger Locator Form.”

Germany is considering major restrictions on international air travel, Interior Minister Horst Seehofer said Tuesday.

“The danger posed by numerous virus mutations forces us to consider drastic measures. That includes significantly stricter border checks, especially at borders with high-risk areas, but also reducing air travel to Germany to almost zero, as Israel is currently doing,” Seehofer told the German newspaper Bild.