An American Airlines passenger plane approaches a landing at LAX during the coronavirus disease (COVID-19) outbreak in Los Angeles, California on April 7, 2021.

Mike Blake | Reuters

Boeing, airlines and other travel stocks soared Monday after health experts shared initial signs that the Omicron variant of Covid may cause milder symptoms than previous strains.

The travel sector was hit hard by the advent of the Omicron variant, which Botswana and South Africa first reported on late last month. Cases were quickly discovered in countries around the world, leading to renewed travel restrictions and outright bans soon after the rules on international travel were relaxed.

Dr. Anthony Fauci, the White House’s senior medical advisor, told CNN on Sunday, “While it’s too early to be definitive, it doesn’t look like it has any great degree of severity yet.” A report by the South African Medical Research Council published on Saturday suggested the strain could be causing a milder infection.

Boeing shares rose more than 3% in afternoon trading on Monday, while American Airlines and United Airlines both rose more than 10% and are among the top winners in the S&P 500, led by Norwegian Cruise Line and Royal Caribbean with gains of 12% and 11%, respectively. The online travel agency Expedia traded more than 8% higher.

However, World Health Organization officials warned on Friday not to read too much into the data on the original cases in South Africa, saying it was too early to understand the severity of the disease caused by Omicron. Early reports of mild symptoms in some of the first cases it was identified were based on a group of university students who tend to be younger and have milder symptoms than older adults, she said. Americans and Europeans also tend to be older and less healthy than the general population in South Africa, they found.

“There have been initial reports that it has tended to be milder, but it’s really too early,” said Maria Van Kerkhove, WHO technical director on Covid-19, in a Q&A streamed on the group’s social media channels became. “Everyone who is infected with SARS-CoV-2, regardless of the variant, always starts with a mild illness. And so it might stop with a mild illness, some people are naturally asymptomatic, but it can stop with a mild illness or something “can take some time”.

Air traffic jumped over the Thanksgiving holiday week, giving airlines some of their busiest days since the pandemic began, although they are still below 2019 levels. Omicron soared on concerns about collapse in demand.

Large network airlines are particularly reliant on long-haul international travel, which was slower to return than domestic travel in the US during the pandemic.

– CNBC’s Holly Ellyatt contributed to this report.