Protesters without face masks attend an anti-restriction rally in Vancouver, British Columbia, Canada, on Oct. 17, 2020. Thousands of protesters took part in the anti-coronavirus-restriction rally to express their disapproval over a number of topics including lockdowns, mask mandates, quarantine, travel bans and social distancing. (Photo by Liang Sen/Xinhua)

Fears over the impact of the Omicron variant of the coronavirus rose on Thursday after the first case was reported in the US and the Japanese central bank warned of economic pain as countries respond with tighter containment measures.

The first known US case was a fully vaccinated person in California who returned to the US from South Africa on November 22 and tested positive seven days later.

US President Joe Biden is working on the US strategy for fighting COVID-19 in winter 2021 and sources briefed on the matter told Reuters one step will be extending requirements for travelers to wear masks through mid-March. 

The White House also plans to announce stricter testing rules for international visitors.

Airlines in the US were told to hand over the names of passengers arriving from parts of southern Africa hit by Omicron, according to a US Centers for Disease Control and Prevention letter seen by Reuters.

Much remains unknown about the new variant, which was first found on November 8 in South Africa and has spread to at least two dozen countries.

Top US infectious disease expert Anthony Fauci on Wednesday said it could take two weeks or more to gain insight into how easily the variant spreads, the severity of the illness that it causes, and whether it can evade currently available vaccines.

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.

World Health Organization (WHO) epidemiologist Maria van Kerkhove told a briefing that data should be available "within days" on Omicron's contagiousness.

BioNTech's CEO said the vaccine it makes in a partnership with Pfizer was likely to offer strong protection against severe disease from Omicron.

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.

Key sharemarket indices in Japan and Australia were weaker on Thursday morning after Wall Street's major averages fell more than 1 percent on Wednesday as investors reacted to the first US case and mounting concerns about inflation. 

Bank of Japan board member Hitoshi Suzuki said Japan's economic recovery may miss expectations if the spread of the Omicron variant hurts consumption, or supply bottlenecks persist. 

"If the impact of supply constraints are bigger or lasts longer than expected, there's a risk economic growth may further undershoot expectations" in 2022, Suzuki said.

Reuters