CIS43LS is a monoclonal antibody that was shown to protect against controlledWe conducted a phase 2 trial to assess the safety and efficacy of a single intravenous infusion of CIS43LS againstIn Part B, 330 adults underwent randomization; 110 were assigned to each trial group. The risk of moderate headache was 3.3 times as high with 40 mg of CIS43LS per kilogram as with placebo.CIS43LS was protective against