SP0273

**SP0273** was Sanofi's investigational quadrivalent messenger RNA seasonal influenza vaccine program, developed from the Translate Bio mRNA platform. It used mRNAs encoding influenza hemagglutinin antigens to induce humoral and cellular immune responses against influenza A and influenza B viruses following intramuscular administration. The program included MRT5407 and MRT5410 clinical candidates evaluated in Phase 1/2 studies in adults. Sanofi identified a need to improve influenza B-strain immune responses and subsequently removed SP0273 from development. ([clinicaltrials.gov](https://clinicaltrials.gov/study/NCT05553301))