Maternal immune response and neonatal seroprotection from a single dose of a monovalent nonadjuvanted 2009 influenza A(H1N1) vaccine: a single-group trial.

BACKGROUND

Pregnant women and infants who get influenza are at increased risk for severe illness.

OBJECTIVE

To evaluate the immunogenicity and transplacental antibody transfer of 2009 pandemic influenza A(H1N1) vaccine administered during pregnancy.

DESIGN

Prospective, multicenter, single-group clinical trial. (ClinicalTrials.gov registration number: NCT01024400)

SETTING

Five level-3 perinatal centers in France.

PATIENTS

107 pregnant women between 22(0/7) and 32(0/7) weeks of gestation.

INTERVENTION

An intramuscular dose of a nonadjuvanted H1N1 vaccine that contained 15 mcg of hemagglutinin.

MEASUREMENTS

Proportion of women with an influenza antibody titer of 1:40 or greater at days 21 and 42 after vaccination, delivery, and 3 months after delivery. Seroconversion rate, fold increase in the geometric mean titer 21 days after vaccination, and proportion of neonates with an antibody titer of 1:40 or greater at birth were also assessed.

RESULTS

At baseline, 19% of the women had an antibody titer of 1:40 or greater. At day 21, 98% of the women had an antibody titer of 1:40 or greater, the seroconversion rate was 93%, and the fold increase in geometric mean titer was 67.4. At day 42, delivery, and 3 months after delivery, 98%, 92%, and 90% of the women, respectively, had an antibody titer of 1:40 or greater. Ninety-five percent of the cord serum samples obtained from 88 neonates showed an antibody titer of 1:40 or greater. The median neonate-mother antibody titer ratio was 1.4.

LIMITATIONS

Only healthy pregnant women were selected. Data on hemagglutination inhibition antibody titers of infants were reported only at birth.

CONCLUSION

A single dose of a nonadjuvanted influenza A(H1N1) vaccine with 15 mcg of hemagglutinin triggered a strong immune response in pregnant women and a high rate of neonatal seroprotection.

PRIMARY FUNDING SOURCE

French National Institute of Health and Medical Research.