The objective of this study is to evaluate the safety and immunogenicity of different vaccines of hemagglutinin formulations of trivalent influenza vaccine or of a combined respiratory syncytial virus / human metapneumovirus / parainfluenza virus type 3 vaccine in healthy participants 18 to 49 years of age. A lipid nanoparticle will be used in this study.

Overall, the study is designed to:

• Assess the safety profile of the candidate formulations
• Describe the immunogenicity profile of the candidate formulations
• Eligible participants will be randomized to receive a single intramuscular injection of either one of the vaccine formulations.

Participants will be provided with a diary to solicit reporting of injection site reactions and systemic reactions, unsolicited Adverse Events (AEs), Serious Adverse Events (SAEs) and Adverse Events of Special Interest AESIs).

Participants will also be required to record their daily temperature on the diary.

The duration of study participation will be approximately 6 months for each participant.

Inclusion Criteria:

• Aged 18 to 49 years on the day of inclusion

• A female participant is eligible to participate if she is not pregnant or breastfeeding and one of the following conditions applies:

  • Is of non-childbearing potential. To be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year, or surgically sterile OR
  • Is of childbearing potential and agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to study intervention administration until at least 4 weeks after study intervention administration.

Exclusion Criteria:

- Any medical condition or circumstance which, in the opinion of the investigator, might interfere with the evaluation of the study objectives

Note: The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org