Inclusion Criteria :
- 18 years of age and above on the day of inclusion
- Provision of informed consent form signed by the participant. If the participant is illiterate, an independent witness is required to sign the consent form.
- Participant able to attend all scheduled visits and comply with all trial procedures
- For a female, if sexually active, use of an effective method of contraception or abstinence for at least 4 weeks prior to the first vaccination, until at least 4 weeks after the last vaccination.
Exclusion Criteria :
- Participation in another clinical trial investigating a vaccine, drug, medical device, or medical procedure in the 4 weeks preceding the trial vaccination
- Planned participation in another clinical trial during the present trial period
- Receipt of any vaccine in the 4 weeks preceding the trial vaccination
- Planned receipt of any vaccine during the study period (except 6 months follow up)
- Receipt of blood or blood-derived products in the past 3 months, which might interfere with assessment of the immune response
- Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months)
- Known seropositivity for human immunodeficiency virus, hepatitis B, or hepatitis C as reported by the participant / parent or legal representative and/or based on medical history
- Known systemic hypersensitivity to any of the vaccine components, or history of a life-threatening reaction to the vaccine(s) used in the trial or to a vaccine containing any of the same substances
- Known thrombocytopenia, contraindicating intramuscular vaccination
- Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating intramuscular vaccination
- Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily
- Chronic illness that, in the opinion of the Investigator, is at a stage where it might interfere with trial conduct or completion
- Employee of the Investigator or study center, with direct involvement in the proposed study or other studies under the direction of that Investigator or study center, as well as family members of the employees or the Investigator
- Previous participation in a trial investigating a vaccine with the swine-origin A/H1N1 influenza strain
- History of influenza infection in 2009-2010
- Receipt of any allergy shots and/or seasonal allergy medication in the 7-day period prior to enrollment (vaccination), or scheduled to receive any allergy shots and/or seasonal allergy medication in the 7-day period after enrollment (vaccination)
- Known pregnancy, or a positive urine pregnancy
- Currently breastfeeding a child
- Current alcohol abuse or drug addiction that might interfere with the ability to comply with trial procedures
Temporary contraindication to be resolved before vaccination:
- Febrile illness (temperature ≥38.0°C) or moderate or severe acute illness/infection on the day of vaccination.