WASHINGTON (BLOOMBERG)- Former advisers to President Joe Biden said travel restrictions will do little to stop the spread of new Covid-19 variants, and the US and other nations would be better off increasing vaccine deliveries to Africa.

Mr Biden last week imposed a broad entry ban on people who have been in South Africa and seven nearby countries, seeking to halt the spread of the Omicron variant. The European Union, the UK, Canada and others have imposed similar measures.

Mr Biden's ban kicks in Monday (Nov 29). While political leaders gravitate to border closures as a way to take immediate action, medical experts tend to say that partial closures are typically ineffective, in part because they affect only a sliver of travel volume.

Mr Andy Slavitt, who served as a Covid-19 adviser to Mr Biden for several months this year, is among the critics and said energy should instead be focused on inoculations in Africa.

"Banning travel hasn't seemed to be anything close to Panacea," Mr Slavitt tweeted on Friday. "And it punishes countries and their economies who make and report discoveries."

He added Saturday: "A far better response would be the mass shipment of hundreds of millions of vaccines to the area."

South Africa's discovery of the variant triggered a market sell-off on Friday. Airlines sank and the S&P 500 closed 2.3 per cent lower, the biggest one-day drop since February.

Middle East stocks tumbled on Sunday, even as South African health officials said initial Omicron cases have been mild.

Dr Anthony Fauci, Mr Biden's chief medical adviser, said Sunday that travel bans would "never completely" prevent a highly transmissible virus from entering the country. "But what you can do is you can delay it enough to get us better prepared," he said on ABC's "This Week."

Dr Francis Collins, head of the National Institutes of Health, told "Fox News Sunday" that travellers entering the US still must be tested, and foreigners entering the US must be vaccinated. He called the curbs a "temporary" measure.

"This is just the best advice of the public health experts. And you'll notice other countries like the UK and the EU are doing the same," he said. "We're not going to say this is going to be there for a long time to block travel from those countries where we know Omicron is already spreading."

The White House, when asked for comment, referred to the remarks by Dr Fauci and Dr Collins. Still, the measure was criticised as modestly effective at best.

Italy's first known Omicron carrier, for instance, arrived two weeks ago, had a negative test before his flight and moved around Italy for days before his diagnosis.

"Travel bans have not been very effective this entire pandemic," Dr Peter Hotez, a professor and dean of tropical medicine at Baylor College of Medicine, told CNN. "I think much more productive than travel bans would be refocusing our energies on trying to vaccinate southern Africa."

Dr Celine Gounder, a physician who served as a Covid-19 adviser to the Biden transition team, said the bans announced by Mr Biden on Friday were too slow and have "massive loopholes."

That includes a lack of bans on Belgium and other countries where cases have been detected, and that US citizens are exempt, she said.

Dr Rick Bright, a former head of the US Biomedical Advanced Research and Development Authority who also advised the transition team, echoed that.

"Porous travel bans will do very little to slow the spread of an airborne virus (replay the tape)," Dr Bright, who now heads the Rockefeller Foundation's Pandemic Prevention Institute, tweeted on Sunday. "The US and world should be getting vaccine and resources to vaccinate people across Africa."

Mr Biden said Friday that the move was precautionary. He called on other nations to boost donations and support a US call for an intellectual property waiver for Covid-19 vaccines.

The US has pledged donations of over 1 billion doses of vaccines by mid-2022, but hasn't pledged anything new for Africa since Omicron's emergence.

'Can't hide'

Mr Biden dismissed a question on Friday about whether travel restrictions discourage countries from coming forward about new variants.

"I'd say that's ridiculous, because you can't hide the variants," he said in Nantucket, where he spent the Thanksgiving holiday with his family. "It's not like someone could hide the fact that there's a new variant with people getting sick more quickly."

Dr Gounder disagreed. "When we punish countries (e.g. South Africa) who've been scientifically transparent and collaborative… how do we think they and others (e.g. China) will behave in the future?" she tweeted.

Mr Slavitt said testing people on arrival and requiring quarantine for positive cases is "sensible."

The US measures reimposed country-based restrictions that were abandoned earlier this month in favour of a system based on whether a traveller is vaccinated or not - regardless of which country they were coming from or recently visited.

The US now has a hybrid system that leaves it largely open to vaccinated foreigners and fully open to citizens, while banning anyone, vaccinated or not, who has been in the eight African countries within the past two weeks.