A new Covid-19 variant, officially named ‘Omicron,’ has doctors and scientists worried that it could evade vaccines and pose an even greater health concern than the Delta strain.

Omicron, first detected in several African countries, has over two dozen mutations in its spike proteins, which could affect transmissibility and the body’s immune response to it. B.1.1.529, as the variant is officially called, is considered the most significant one yet and scientists are working around the clock to determine whether it renders vaccines useless.

In an interview, one scientist called the new strain “horrific,” saying that it was worse than anything that has yet been seen.

The United States has imposed new travel restrictions from South Africa and seven other countries – Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique, and Malawi – starting Monday due to the new concerning variant, with President Biden making the decision after being briefed by White House chief medical advisor Dr. Anthony Fauci.

The decision comes less than three weeks after Biden lifted travel restrictions on more than 30 countries, including South Africa, in favor of instead simply requiring travelers to be vaccinated. The new travel restrictions disregard travelers’ vaccination status.

Israel, which opened its borders to tourists on November 1st, is closing their doors yet again due to the Omicron strain. The new travel ban will be in effect for at least 14 days, beginning Sunday night at midnight. The new travel ban is expected to hamper Chanukah travel plans for many Americans and Israelis living abroad, who are likely to be locked out of the country for at least two weeks.