Safety and Immunogenicity of the Butantan Institute Influenza Vaccine Compared to Sanofi Pasteur Influenza Vaccine

Inclusion Criteria: * Adult, male or female, age 18 to 69 years (inclusive) at the time of enrollment; * Provide written informed consent; * Agrees to complete all study visits, procedures and contacts; Exclusion Criteria: * Chronic medical conditions such as psychiatric conditions, diabetes, hypertension or any other conditions that might place the subjects at high risk of adverse events. Study clinicians will use clinical judgment on a case-by-case basis to assess safety risks under this criterion; * Clinically significant abnormalities on physical examination; * Use of immunosuppressive medications such as systemic corticosteroids or chemotherapeutics, or immunosuppressive illness. It will be considered immunosuppressive dose of systemic corticosteroids the equivalent to a dose ≥10 mg of prednisone per day for over 14 days; * Women who report being pregnant or have plans to become pregnant during the study period; * Participation in research involving another investigational product within 30 days before planned date of first vaccination or anytime through the last study safety visit; * Acute febrile illness (axilar temperature ≥ 37.8°C); * Hypersensitivity to egg or chicken proteins; * History of Guillain-Barre Syndrome; * Thrombocytopenia or a bleeding disorder contraindicating intramuscular vaccination; * Unstable chronic illness (defined as illness requiring hospitalization or a clinically significant change in medication in the previous 12 weeks); * Alcohol abuse or drug addiction; * Any vaccination within the previous 4 weeks; * Seasonal influenza vaccination in the previous 6 months.