Approximately one billion cases of seasonal influenza occur annually. Of these, 3 to 5 million illnesses are severe and responsible for up to 650,000 deaths per year (WHO 2025). Yearly administration of an influenza vaccine for the prevention of influenza is currently recommended. However, the real-world vaccine effectiveness varied from 10% to 60% in the general population across the years of 2004 to 2024, with effectiveness in most years below 50% (CDC 2025) and decreasing to as low as 5% in immunocompromised individuals (Hughes 2021). The goal of this study is to learn whether MK-1406 (CD388) can help prevent the flu in people who are at higher risk of becoming seriously ill from influenza. Researchers want to find out if MK-1406 dosed at a single study visit can provide protection against influenza compared with placebo. The study will include adolescents and adults who may be more vulnerable to complications from influenza because of their age, health conditions, or weakened immune systems. Researchers will also evaluate the safety of MK-1406 and how well participants tolerate the study medicine.
Phase 3 trials are pivotal studies with large patient populations (hundreds to thousands) designed to prove efficacy and safety for FDA submission. A successful Phase 3 readout is typically the last major hurdle before a New Drug Application (NDA) or BLA filing.
Enrollment is complete. The trial is in its follow-up or data collection phase — a readout may occur on or near the primary completion date.
Cidara Therapeutics (CDTX) is the sponsoring company for this trial. BiotechSign currently grades this company F (26/100) based on composite catalyst signals across its full pipeline. This trial is one data point in that overall catalyst picture.