Twitter CEO and co-founder Jack Dorsey gestures while interacting with students at the Indian Institute of Technology (IIT) in New Delhi on November 12, 2018. Check out the companies making headlines in midday trading Monday: Moderna — Moderna shares surged more than 9% after CEO Stephane Bancel said Monday it will take months to distribute a Covid vaccine specifically targeting the omicron variant, but a higher 100-microgram dose of the booster shot could be ready "right away." Bancel said it will take at least two weeks to study how the new variant's mutations impact the efficacy of current vaccines. Twitter — Shares of the social media company fell about 1% after news that CEO Jack Dorsey is stepping down, effective immediately. Parag Agrawal, the company's chief technology officer, will take over as chief executive. Dorsey was serving as both the CEO of Twitter and Square, his digital payments company. He will remain a member of the board until his term expires in 2022. Merck — Shares of the pharmaceutical giant slide 4.5% after Citi downgraded Merck to neutral from buy. Citi said in a note to clients that disappointing data from two key drugs for Merck in recent weeks hurt its long-term earnings potential. Ebay — The e-commerce giant lost more than 2% after announcing it's acquiring Sneaker Con Digital, the sneaker authentication business of the marketplace Sneaker Con. Ebay said the deal furthers its expansion strategy in sneakers and will give customers added confidence in their high-value item purchases. The companies signed and closed the deal on Nov. 24. Terms of the . . . read the full article here.