The Use PUL‐042 inhalation solution to prevent COVID‐19 in adults exposed to SARS‐CoV‐2  Drug: PUL‐042 inhalation solution, drug: placebo  COVID‐19  200, all, 18 years and older  Treatment  Experimental: PUL‐042 inhalation solution, PUL‐042 inhalation solution (20.3 µg Pam2: