There’s a new COVID-19 variant first identified in South Africa that’s concerning health experts around the world.

A World Health Organization advisory panel has classified it as a highly transmissible variant of concern and already named it ”omicron” under its Greek letter system.

The Delta variant, which has become the world’s most prevalent, is in the same category.

The so-called B.1.1.529 variant has caused stock markets to plunge and led the 27-member European Union and some other countries to  suspend travel flights to and from southern Africa.

”We don’t know very much about this, yet.  What we do know is that this variant has large number of mutations, and the concern is that when you have so many mutations it can have an impact on how the virus behaves,” according to Maria van Kerkhove, WHO’s top technical COVID expert.

”It will take a few weeks for us to understand what impact this variant has on any potential vaccines, for example.”

While experts, including those from the World Health Organization, caution against any overreaction before more is known, but countries say their actions, including the banning of flights from countries of concern, are justified.

British Health Secretary Sajid Javid says ”We must move quickly and at the earliest possible moment.”

The U.K.’s announced it’s banning flights from South Africa and five other southern African countries, and anyone who’d recently arrived from those countries would be asked to take a test.