The Safety and Immune Response to Influenza Vaccination in Pregnant Women

Inclusion Criteria: 1. Pregnant female aged ≥ 18 years old. 2. Subject is pregnant for at least 3 months, inclusive. 3. Subject is willing and able to adhere to visit schedules and all study requirements. 4. Subject has read and signed the study-specific informed consent. Exclusion Criteria: 1. Subject with previous complicated pregnancy or preterm delivery, spontaneous or medical abortion; 2. Subject with history or concurrent high risk of dangerous gestation such as gestational diabetes mellitus (GDM), pregnant induced hypertension, or preeclampsia; 3. Subject received any influenza vaccine within the previous 6 months; 4. Subject has a history of hypersensitivity to eggs or egg protein or similar pharmacological effects to study vaccine; 5. Subject or her family has the history of Guillain-Barré Syndrome; 6. Subject has current upper respiratory illness (URI), including the common cold or nasal congestion within 72 hours; 7. Subject with influenza-like illness as defined by the presence of fever (temperature over 38ºC) and at least two of the following four symptoms: headache, muscle/joint aches and pains (e.g. myalgia/arthralgia), sore throat and cough; 8. Subject receive any treatment with an investigational drug or device, or participation in a clinical study, within 3 months before consent; 9. Subject has immunodeficiency or is under immunosuppressive treatment. 10. Subject received any vaccine within 1 week prior to study vaccination or expected to receive one within 1 week after study vaccination; 11. Subject received any blood products, including immunoglobulin, in the past 3 months before consent; 12. Subject has underlying condition in the investigators' opinion may interfere with evaluation of the vaccine;