Shares of Altimmune Inc. ALT were down 4.8% in trading on Thursday after the company said it started enrolling participants in a Phase 1 clinical trial for its COVID-19 vaccine candidate. Altimmune is developing a single-dose nasal spray vaccine. The study is expected to enroll up to 180 healthy adults between the ages of 18 and 55 years old, who will receive one of three doses of the experimental vaccine. The company said it expects to share the first batch of clinical data from this trial in the second quarter of this year. Altimmune's stock has soared 969.9% over the past 12 months, while the broader S&P 500 SPX is up 21.7%.