Heavily mutated Omicron is rapidly becoming the dominant variant of the Covid-19 in South Africa less than four weeks after it was first detected there, as the United States joined the list of countries which have identified cases of the variant.
The first known US case was a fully-vaccinated person in California who returned to the country from South Africa on November 22nd and tested positive seven days later.
The person had mild symptoms and was in self-quarantine, Dr Anthony Fauci, the top US infectious disease official, told reporters at the White House.
Key questions remain about the new variant, which has been found in two dozen countries, including Ireland, the UK, Spain, Canada, Austria and Portugal. The first case of the variant was detected in Ireland on Wednesday, the National Public Health Emergency Team (Nphet) confirmed.
Early indications suggesting Omicron may be markedly more contagious than previous variants have rattled financial markets, fearful that new restrictions could choke off a tentative recovery from the economic ravages of the pandemic.
South Africa's National Institute for Communicable Diseases (NICD) said early epidemiological data suggested Omicron was able to evade some immunity, but existing vaccines should still protect against severe disease and death.
It said 74 per cent of all the virus genomes it had sequenced last month had been of the new variant, which was first found in a sample taken on November 8th in Gauteng, South Africa's most populous province.
The number of new cases reported in South Africa doubled from Tuesday to Wednesday.
World Health Organisation (WHO) epidemiologist Maria van Kerkhove told a briefing that data on how contagious Omicron was should be available "within days."
BioNTech's chief executive said the vaccine it makes in a partnership with Pfizer was likely to offer strong protection against severe disease from Omicron.
'Prepare for the worst'
The president of the European Union's executive body said there was a "race against time" to stave off the new variant while scientists establish how dangerous it is. The EU brought forward the start of its vaccine rollout for five to 11-year-olds by a week to December 13th.
"Prepare for the worst, hope for the best," Ursula von der Leyen, president of the European Commission, told a news conference.
She said full vaccination and a booster shot provided the strongest possible protection, according to scientists - a view echoed by Dr Fauci in the US.
But WHO emergencies director Mike Ryan criticised developed countries pushing booster shots for large parts of their fully vaccinated populations when vulnerable people in many poorer regions have had no vaccination at all.
"There is no evidence that I'm aware of that will suggest that boosting the entire population is going to necessarily provide any greater protection for otherwise healthy individuals against hospitalisation or death," he said.
The WHO has noted many times that Covid will keep producing new variants for as long as it is allowed to circulate freely in large unvaccinated populations.
Travel restrictions
Some 56 countries, including Ireland, were reportedly implementing travel measures to guard against Omicron as of November 28th, the WHO said.
UN secretary-general Antonio Guterres slammed what he called "travel apartheid."
"Blanket travel bans will not prevent the international spread and they place a heavy burden on lives and livelihoods," the WHO said, while advising those who were unwell, at risk, or 60 years and over and unvaccinated to postpone travel.
