Governments around the world rushed to contain a new, heavily mutated Covid-19 strain on Sunday, with Israel slamming its borders shut to foreign nationals and Australia reporting its first cases of the variant.

The variant now known as Omicron has cast doubt on global efforts to fight the pandemic because of fears that it is highly infectious, forcing countries to reimpose measures many had hoped were a thing of the past.

Scientists are racing to determine the threat posed by the heavily mutated strain — particularly whether it can evade existing vaccines.

Several countries including Pakistan, Saudi Arabia and Qatar have also announced plans to restrict travel from southern Africa, where it was first detected.

Pakistan’s National Command and Operation Centre (NCOC) on Saturday placed a complete ban on travel from six south African countries and Hong Kong in the wake of the discovery of the new variant.

The notification said travel had been restricted from South Africa, Lesotho, Eswatini, Mozambique, Botswana and Namibia as well as Hong Kong.

These countries, the NCOC added, had been placed in category C — which includes nations from where people face restrictions and can only travel to Pakistan under specific NCOC guidelines — consequent to the emergence of the Omicron strain in South Africa and its spread to adjoining regions.

The strictest announcement, however, came from Israel, which said on Sunday it would close its borders to all foreigners in a bid to curb the spread of the variant — just four weeks after reopening to tourists after a prolonged closure due to Covid-19.

“We are raising a red flag,” Israeli Prime Minister Naftali Bennett said, adding that the country would order 10 million PCR test kits to stem the “very dangerous” strain.

Israeli citizens will be required to present a negative PCR test and quarantine for three days if they have been vaccinated against the coronavirus and seven days if they have not, the prime minister’s office said.