Participants in this study will be given either CC-42344 (one of two dose levels) or placebo orally for 5 days after receiving an influenza (flu) challenge virus. Participants will not know whether they are getting placebo or CC-42344. The amount of virus in nasal samples will be measured over time. Side effects and pharmacokinetics (the amount of CC-42344 in blood) will also be measured.

This is a single-center, phase 2a, randomized, double-blind, placebo-controlled study in healthy adult participants. The primary goal of this study is to assess the antiviral activity of orally administered CC-42344 in an influenza human viral challenge model, and to explore the impact of different dose levels on efficacy. In addition, the safety, tolerability, and pharmacokinetics will be assessed.

Inclusion Criteria:

• Healthy adults
• Body weight ≥50 kg
• Body mass index ≥18 kg/m2 and ≤35 kg/m2
• Serology results consistent with susceptibility to challenge virus infection

Exclusion Criteria:

• History of or current significant medical condition
• Upper or lower respiratory tract infection within 4 weeks
• Vaccination within 4 weeks