Effectiveness of an influenza A (H1N1) 2009 monovalent vaccine among Japanese pregnant women: A prospective observational study assessing antibody efficacy
ABSTRACT In order to estimate the effectiveness of an influenza A (H1N1) 2009 monovalent vaccine among pregnant women, we prospectively observed 135 Japanese pregnant women who received an influenza A (H1N1) 2009 monovalent vaccine during November 2009. We calculated an index of "antibody efficacy", in which the medical visits for respiratory illnesses were compared between those with and without post-vaccination hemagglutination inhibition (HI) titer ≥1:40. The product of antibody efficacy and achievement rate is theoretically equivalent to the vaccine effectiveness. Among all subjects, an inverse but non-significant relationship during the epidemic period was observed between post-vaccination HI titer ≥1:40 and medical visits for respiratory illnesses. After stratification by trimester at recruitment, a significant inverse association during the epidemic period was found among subjects in the first or second trimester (antibody efficacy: 91%, vaccine effectiveness: 79%). The influenza A (H1N1) 2009 monovalent vaccine administered in the first or second trimester reduced medical visits for respiratory illnesses among Japanese pregnant women.
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ABSTRACT: To monitor and evaluate the safety of the influenza A (H1N1) vaccine in pregnant women and its influence on the fetus and neonate, we performed a prospective study in which 122 Chinese pregnant women who received the influenza A (H1N1) vaccine and 104 pregnant women who did not receive any vaccine as control were observed. The results indicated that the seroconversion rate in the vaccinated group was 90.4% (95%CI: 82.6-95.5%). The rate of adverse events following immunization in the pregnant women who received the influenza A (H1N1) vaccine was 3.3%. The spontaneous abortion rates of the vaccinated group and unvaccinated group were 0.8% and 1.9%, respectively (exact probability test, p= 0.470); prolonged pregnancy rates were 8.2% and 4.8%, respectively (χ(2)=1.041, p=0.308); low birth weight rates were 1.6% and 0.95%, respectively (exact probability test, p = 1.000); and spontaneous labor rates were 70.5% and 75%, respectively (χ(2)= 0.573, р=0.449). All newborns that received an Apgar score of 7 or more are healthy. Apgar scores of 9 and above were observed in 38.5% and 57.7% of newborns in the vaccinated group and the unvaccinated group, respectively (χ(2)= 8.274, p=0.004). From these results, we conclude that the influenza A (H1N1) vaccine is safe for pregnant women and has no observed adverse effects on fetal growth. CLINICALTRIALS.GOV Identifier: NCT01842997.Clinical and vaccine Immunology: CVI 07/2014; 21(9). DOI:10.1128/CVI.00375-14 · 2.37 Impact Factor