Fears over the impact of the Omicron variant of the coronavirus rose on Thursday after the first case was reported in the United States .
The first known U.S. case was a fully vaccinated person in California who returned to the United States from South Africa on Nov. 22 and tested positive seven days later .
Reports say that the White House is also planning to announce stricter testing rules for international visitors.
Airlines in the United States were told to hand over the names of passengers arriving from parts of southern Africa hit by Omicron.
Top U.S. infectious disease expert Anthony Fauci on Wednesday said it could take two weeks or more to gain insight into how easily the variant spreads.
He also says the severity of the illness that it causes, and whether it can evade currently available vaccines is not yet known.
South Africa’s President Cyril Ramaphosa also said he was “deeply disappointed” by the travel bans, which he described as being unjustified.
Most of the people who have been hospitalized in South Africa had not been vaccinated against coronavirus, according to the NICD.
WHO chief Tedros Adhanom Ghebreyesus later warned that blanket Covid measures were penalizing southern Africa countries .