Rise and fall of serum HI antibody induced by 2009 influenza A(H1N1) vaccine

In order to investigate the rise and fall of serum HI antibody induced by 2009 influenza A(H1N1) vaccine to provide evidence for immunization strategy,serum specimen were collected from 128 vaccine recipients at the 3 rd,6 th,9 th and 12 th month after vaccination.Antibody titres were measured with haemagglutination inhibition(HI) assay.The positive rates in 128 recipients at the 3rd,6th,9th and 12th month were 61.7%,47.7%,40.9% and 35.43%,respectively;and the geometric mean titers(GMTs) of HI antibody were 40,28.4,24.5,and 23.6,respectively;both differences were significant(P0.01).The positive rates and GMTs were significantly decreased with time in both male and female(P0.01),and GMTs were significantly decreased in all age groups as well(P0.01).For 79 subjects with positive HI antibody,the positive rates at the 3rd,6th,9th and 12th month were 100%,75.95%,64.56% and 54.43%;GMTs were 104.09,58.33,45.23 and 41.82,respectively;and the differences were significant(P0.01).No matter gender or age,the positive rates and GMTs were significantly decreased with time(P0.01).The data suggest that the levels of HI antibody induced by 2009 influenza A(H1N1) vaccine decline rapidly and the immunogenicity is not lasting.