** Shares of drug developer Upstream Bio UPB.O rise 20% to $32.64 in premarket trading

** Company says its experimental asthma drug, Verekitug, reduced severe asthma attacks in a mid‑stage study

** The drug reduced yearly asthma flare‑ups by 56% at a lower dose and 39% at a higher dose, and improved lung function - UPB

** Side-effects were similar to earlier studies; over 90% of eligible patients entered a long‑term extension study, company says

** UPB plans late‑stage trials in severe asthma and chronic sinus disease after talks with regulators

** Shares up ~65% in 2025