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.
