Take a look at the top companies in Tuesday’s midday trading.

American Airlines, Norwegian Cruise Line — Travel stocks retreated, as investors continued to weigh the risks from the Covid omicron variant. American Airlines shares plunged more than 4.4%; Norwegian Cruise Line fell over 6%; Wynn Resorts dropped roughly 5%; and Airbnb plummeted 4.9%

Gap, Under Armour — Retail stock were under pressure after Cyber Monday online sales dropped 1.4% from last year, falling for the first time ever, according to Adobe Analytics. Adobe is confident that this holiday season, which will record new sales records online, customers are spreading their shopping. Under Armour fell by 6% and Gap dropped more than 6%. Tommy Hilfiger was parent. PVH CorpYou have lost over 4%

Regeneron Pharmaceuticals — Regeneron shares fell more than 2% after the company said its Covid-19 antibody drugs could be less effective against the omicron Covid variant. The company said mutations in the variant suggest “there may be reduced neutralization activity of both vaccine-induced and monoclonal antibody conveyed immunity.”

Moderna, Pfizer — Shares of vaccine makers were in focus after Moderna CEO Stephane Bancel told The Financial Times he expects existing vaccines to be less effective against the omicron variant. Oxford University has confirmed that there is no prior immunity to the reaction of this new variant. Researchers continue to study it. no evidence yet that current vaccines will not protect against severe disease from omicron. Moderna shares plunged more than 6%. BioNTech shares dropped more than 5%. Pfizer shares rose by about 2%. Novavax shares gained more than 2%

Dollar Tree — The discount retailer’s stock slid 4.5% after Goldman Sachs downgraded Dollar TreeNeutral from Buy According to the firm, the operational improvements made by the company were already priced in and Dollar Tree will struggle to attract foot traffic in the coming year.

Solaredge — The clean energy stock shed 6.3% after Morgan Stanley downgraded it to equal-weight. In a note sent to clients, the investment company stated that Solaredge shares could be fully valued following a hot streak.

Meta Platforms — Facebook-parent Meta’s shares fell more than 3% after the U.K. competition watchdog said the company should sell the GIF-sharing platform GiphyFacebook bought the company last year. It was feared that the agreement could cause harm to social media users as well as U.K. advertisers. Meta said that it disapproves of the decision and is looking into appealing.

Beyond Meat, Oatly — Shares of Beyond Meat and Oatly retreated roughly than 6% and 7%, respectively, after HSBC initiated coverage of the protein stocks at a reduce rating. According to the firm, “Given increased competition we expect the growth will not be enough for many participants in achieving their lofty goals of growth,”

Twitter, Square — Shares of Twitter and Square retreated more than 5% and 2%, respectively. These moves came a day later Jack Dorsey announced he is stepping down as CEO of TwitterWhile remaining as Square’s chief executive officer. Bank of America upgraded Square to neutral from underperform and reiterate a buy rating for Twitter.

— CNBC’s Jesse Pound and Tanaya Macheel contributed reporting