Changes of haemagglutination inhibition antibody level within one month after influenza A （ HIN1 ）vaccination
Objective To find the changes of haemagglutination inhibition （ HI ） antibody level against A/California/07/2009 （H1N1） within one month after pandemic A/H1N1 influenza vaccine （A/H1N1InfV） vaccination, and to provide data for drawing up immunization protocols against novel influenza . Methods The HI antibodies against A/California/07/2009 （H1N1） in sera from the inoculated subjects were tested by HI test .The geometric mean titer （ GMT） , geometric mean increase （ GMI） , seroconversion （SC） rate, seroprotection （SP） rate of HI antibodies were compared among the sera collected on day 3, 7, 14, 30 post vaccination .Results 961 participants were injected with A/H1N1InfV.In subjects aged 3 to 11 years, the antibody level peaked on day 14 post vaccination, but neither on day 14 nor on day 30, the lower bound of the two -sided 95%CI for the SP rate could fulfill the criteria of the FDA for influenza vac-cine.In subjects aged 12 to 60 years, the antibody level peaked on day 14 post vaccination and the SC rate , SP rate and GMI fulfilled the criteria of the European Medicines Agency （ EMEA） and the FDA for influenza vaccine. In subjects aged more than 60 years, the antibody level peaked on day 30 post vaccination , and the SC rate, SP rate and GMI on day 30 fulfilled the criteria of the EMEA and the FDA .Conclusion One dose A/H1N1InfV vaccination was able to induce enough protection on day 14 for subjects aged 12 to 60 years, on day 30 for subjects aged more than 60 years;however , for subjects aged 3 to 11 years who were antibody-negative at baseline , the lower bound of the two-sided 95%CI for the SP rate on day 14 and day 30 couldn′t fulfill the criteria of the FDA for influenza vaccine . 
 
Key words: 
Pandemic A/H1N1 influenza vaccine;  Hemagglutination inhibition test;  Changes ofHI antibody level