CHICAGO – Influenza vaccination appears to improve neonatal outcomes, but coverage remains inadequate among pregnant women.
Among 1,641 evaluable women delivering at Duke University Hospital during the 2009-2010 influenza season, receipt of any flu vaccination was significantly associated with higher infant birth weight (3,178 grams vs. 2,903 grams) and longer gestational age (38.3 weeks vs. 36.8 weeks, both P values less than .0001).
©AvailableLight/istockphoto.com
A higher infant birth weight was recorded in pregnant women who received at least one flu vaccine.
Women who received at least one flu vaccine also were significantly less likely to require an antepartum visit or hospital admission than those who did not (39% vs. 44%, P = .005).
"This information supports prior accumulating data that receipt of a flu vaccine improves not only maternal outcomes, but also birth outcomes," Dr. Kimberly Fortner said at the annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology.
In all, 44% of women in the preliminary analysis received both vaccines in compliance with recommendations, far higher than historical influenza vaccination rates of 12%-34% and comparable to other reports from the season. Another 7% elected no vaccine at all, and 24% of the population had no documented receipt of vaccine in obstetrical records or other electronic medical records.
Uptake of seasonal influenza vaccine was 58% vs. 55% for the 2009 H1N1 influenza vaccine, which is unique among published prior literature.
Even though rates were nearly equal, 24% of women elected to receive only one of the two recommended vaccines, resulting in inadequate coverage, said Dr. Fortner of Duke University Medical Center in Durham, N.C.
The researchers hypothesized that pregnant women may have inappropriate or inadequate vaccination during the 2009-2010 flu season due to issues of vaccine distribution, sensationalism of the H1N1 influenza pandemic, and recommendations by the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices that pregnant women receive both the seasonal and H1N1 influenza monovalent vaccines.
The earlier women went in for prenatal care, however, the more likely they were to receive a vaccine, she said.
Mean gestational age at first prenatal visit was significantly lower at 14.8 weeks among women who received the vaccine, compared with 18.6 weeks for women who did not receive any vaccine and 21.2 weeks for those with unknown vaccine status (P less than .0001).
Black women and those with public insurance or no insurance were significantly less likely to receive any vaccine.
In multivariate analysis that adjusted for maternal age, black race, less than a high school education, Medicaid or no insurance, and medical comorbidities, receipt of any influenza vaccine during that season was significantly associated with an estimated 133.7 g increase in birth weight (P = .0003).
Dr. Kimberly Fortner
The association between flu vaccination and preterm birth is unclear but might be explained by the healthy user effect, unidentified confounders or perhaps influenza behaves differently than other viruses. It may activate the inflammatory cascade in different ways, or perhaps the vaccine translates into different mechanisms that are protective, Dr. Fortner said.
Demographic data available on 1,642 women showed that the study population was diverse, with 31.5% black, 31.5% white, 25% Hispanic, 7% Asian/Pacific Islander, and 5% other. The mean maternal age was 28.7 years, 16% had less than a high school education, 28% had a chronic medical condition such as hypertension, diabetes, asthma, or a thrombotic disorder, and 37% received prenatal care at a public health department. Outcome data was not available for one patient.
The study was funded by the 2010 American College of Obstetricians and Gynecologists/Merck & Company Inc. Research Award on Immunization. Dr. Fortner and her colleagues reported no relevant financial disclosures.