The purpose of this study is to evaluate the antibody response in dialysis patents to each of the three influenza vaccine strains included in the licensed seasonal flu vaccine (Formulation 2011-2012).

The immune response to influenza vaccine was poor in dialysis population than general population. The investigators want to evaluate another booster vaccination can improve the immune response in dialysis population. All enrolled participants will be divided into 3 groups: participants refused to receive vaccination, those receive either one (week 0) or one more booster vaccination (week 0 and week 3). The investigators will collect serum of participants 3 weeks, 6 weeks, 9 weeks and 18 weeks post vaccination and evaluate the difference of immune response in these 3 groups.

Inclusion Criteria:

1. Males and non-pregnant females and aged more than 18 years;
2. Willing and able to adhere to visit schedules and all study requirements;
3. Subjects read and signed the study-specific informed consent.

Exclusion Criteria:

1. Subject or his/her family is employed by the participated hospital;
2. Subjects received 2010-2011 seasonal influenza vaccine within the previous 6 months;
3. History of hypersensitivity to eggs or egg protein or similar pharmacological effects to study medication;
4. Personal or family history of Guillain-Barré Syndrome;
5. An acute febrile illness within 1 week prior to vaccination;
6. Current upper respiratory illness, including the common cold or nasal congestion within 72 hours;
7. Subjects with influenza-like illness as defined by the presence of fever (temperature ≥ 38°C) and at least two of the following four symptoms: headache, muscle/joint aches and pains (e.g. myalgia/arthralgia), sore throat and cough;
8. Female subjects who are pregnant during the study.
9. Patients who receive hemodialysis therapy less than 3 months.
10. Treatment with an investigational drug or device, or participation in a clinical study, within 3 months before consent;
11. Immunodeficiency, or under immunosuppressive treatment.
12. Receipt of any vaccine within 1 week prior to study vaccination or expected receipt between Visit 1 (study vaccination) and Visit 2 (final collection of blood samples);
13. Receipt of any blood products, including immunoglobulin in the prior 3 months;
14. Any severe illness needed to be hospitalization within three months.
15. Underlying condition in the investigators' opinion may interfere with evaluation of the vaccine.