637: No association of malformations with first trimester influenza vaccination

Abstract

Limited data are available regarding the use of seasonal influenza vaccination during pregnancy, particularly in the first trimester. We sought to ascertain any association of fetal malformations with first trimester influenza vaccination. This was a population-based surveillance of an antepartum influenza vaccination program. Pregnant women receiving prenatal care from October, 2003 through March, 2008 were offered the seasonal trivalent inactivated influenza vaccine (TIV). TIV was offered in the second and third trimester during the 2003-2004 season: from the 2004-2005 season onward, it was offered in all trimesters. Data were collected on the vaccinated women and entered into an established computerized database. Major and minor malformations were detailed at delivery by the attending pediatric physician. Student's t-test and chi-square analysis were used to determine significance. During the 5-year study period, 8690 women received the seasonal influenza vaccine antepartum; 439 in the first trimester and 8251 in the second or third trimester. Women vaccinated antepartum were significantly older with a higher parity than women who did not receive the vaccine in our prenatal system. They also were significantly more likely to have a medical complication requiring evaluation in our Obstetric Complications Clinic. Infants born to mothers receiving the influenza vaccine in any trimester did not have an increase in major malformations; 10 (2%) in the first trimester vaccination group and 126 (2%) in the second/third trimester group, compared to 2% in women with no reported vaccination. In addition, no significant difference was seen in the rate of minor malformations between the vaccinated group and the women with no reported vaccination. Influenza vaccination in the first trimester was not associated with an increase in major malformation rates. This will aid in counseling women regarding the safety of vaccination in the first trimester.