Dec 20, 2012

Seasonal Flu Vaccine Safe in Early Pregnancy, Study Confirms

NEW YORK (Reuters Health) Dec 20 – A new study provides additional reassurance on the safety of trivalent inactivated influenza vaccine during the first trimester of pregnancy, say researchers with the Vaccine Safety Datalink team in a paper published today.

“We found no increased risk of spontaneous abortion during a four-week exposure window after vaccination. This is important because pregnant women have an increased risk of influenza complications, and vaccination is recommended to protect both the mother and baby,” Dr. Edward Belongia, Director of the Epidemiology Research Center at Marshfield Clinic Research Foundation in Marshfield, Wisconsin, told Reuters Health.

Included in the analysis were 243 women aged 18 to 44 who suffered spontaneous abortion and 243 control women with a live birth matched by healthcare organization and date of last menstrual period.

The primary exposures of interest were the 2005-2006 and 2006-2007 seasonal trivalent inactivated flu vaccines within each matched pair during the 28 days preceding the date of spontaneous abortion.

In the January 2013 issue of Obstetrics & Gynecology, available online today, the researchers say 16 women with spontaneous abortion (7%) and 15 matched controls (6%) received influenza vaccine within the 28-day exposure window.

They found no statistically significant association between spontaneous abortion and influenza vaccination in the 28-day exposure window (adjusted matched odds ratio 1.23; p=0.63).

In 1997, the Centers for Disease Control and Prevention Advisory Committee on Immunization Practices expanded U.S. recommendations for pregnant women to include healthy women in the second or third trimester of pregnancy. (Previously, the ACIP had called for flu vaccines in pregnancy only for women with an underlying high-risk medical condition.) In 2004, the recommendation was further expanded to include pregnant women in any trimester. Current European guidelines also recommend the seasonal vaccination of all pregnant women, regardless of trimester.

Dr. Belongia told Reuters Health, “Several studies have confirmed the safety of influenza vaccine when given in the second or third trimester, but relatively few studies have focused on early pregnancy. Our study substantially strengthens the body of evidence supporting influenza vaccine safety during the first trimester.”


Obstet Gynecol 2012.

— Megan Brooks


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