Traders have upped their bets against several biotech companies, including the beleaguered Novavax. Short interest in Novavax increased more than 13% to 37.8 million shares, or about 45% of the total float, between March 15-31, according to data compiled by FactSet. The float refers to the stocks available for trading. The Covid vaccine-maker raised doubts in February about its ability to stay afloat. Last week, CEO John Jacobs told Reuters it plans to slash about $50 million in costs in the first quarter — with more cuts to follow. Other biotech companies that saw growing short interest are Cassava Sciences , with a 10% increase, and Fate Therapeutics , which saw a 26% boost. That brought both names to about 30% of float. Meanwhile, bluebird bio had a 29% increase in its short interest to 26% of float. Traders were also increasingly bearish on two movie chains. Cinemark and AMC Entertainment both saw increases in their short position to 28% and 27% of their respective floats. Here are the most shorted stocks between March 15-31. All names trade on the NYSE or Nasdaq, have short positions amounting to at least 25% of their total float and have market values of at least $100 million.