** Shares of vaccine developer Vaxcyte PCVX.O down 51% at $34.04, lowest since October 2022

** Company says its experimental pneumococcal vaccine for infants, VAX-24, achieved "non-inferiority" in a mid-stage study compared to rival Pfizer's PFE.N Prevnar 20 shot

** Pneumococcal disease spreads through direct contact with respiratory secretions such as saliva or mucus and can cause fever, cough and chest pain

** Brokerage Guggenheim says the mid-stage data was consistent with co's expectations, but didn't meet high investor expectations, adding that the vaccine's immune response seems to be lower in children compared to adults

** Brokerage Jefferies says the stock pullback is mostly driven by the political headwind and anticipation of the data

** Jefferies also points to the "continued unfavorable market environment, particularly recent resignation of FDA CBER director who oversees vaccine"

** Shares of vaccine makers and other biotech companies have been falling as Wall Street Journal and other media outlets reported on Friday that Peter Marks, a top vaccine official at the U.S. FDA, has been pushed out of the agency

** Stock had fallen 62.4% YTD

(Reporting by Siddhi Mahatole)

((siddhi.mahatole@thomsonreuters.com))