(Bloomberg) -- Shares of online travel companies, including Booking Holdings Inc. and Expedia Group Inc., fell the most since the earliest days of the Covid-19 pandemic over worries about a new, heavily-mutated variant of the virus.

Expedia plummeted as much as 11.9%, the most since March 2020, placing it among the 10-worst-performing stocks in the S&P 500 Friday, according to data compiled by Bloomberg. Booking fell as much as 9.6%.

Fears of the variant, known as B.1.1.529, spread widely through governments and stock markets, putting pressure on travel and airline stocks. The U.K. has already instituted travel restrictions on arrivals from South Africa and its neighboring countries, where the variant was first identified.

The Bloomberg EMEA Airlines Index experienced its biggest drop since the beginning of the pandemic. Booking Chief Executive Officer Glenn Fogel told analysts and investors early this month that rising Covid cases in Europe “adds to the uncertainty around how November and December trends will progress.”

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