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Study finds no evidence of harm to infant development after mothers get flu vaccine while pregnant

Kaiser Permanente study supports safety of vaccinating pregnant women, who face higher influenza risks


A Kaiser Permanente study of women who were given inactivated influenza vaccine while pregnant found no indication of developmental problems for their babies at 6 months old. The findings were published Feb. 5 in the journal Vaccine.

“This study offers additional confirmation of the safety of the influenza vaccine for both pregnant women and their children,” said lead author Lyndsay Avalos, PhD, MPH, an investigator with the Kaiser Permanente Division of Research.

Lyndsay Avalos, PhD, MPH the study’s lead author and a research scientist at the Division of Research

“We’re in the middle of a severe flu season and there is time for women to protect themselves and their babies with a flu shot,” said Kari Carlson, MD, chief of the department of obstetrics and gynecology at Kaiser Permanente in Redwood City. “Not enough pregnant women get vaccinated, possibly because of misconceptions about safety. But having the flu presents unique health risks to pregnant women.”

The study focused on 1,225 mothers who were Kaiser Permanente members and filled out the Ages & Stages Questionnaire (ASQ-3) about the health of their infants at 6 months old. The ASQ-3 is a common tool used in clinical practice to screen for developmental delays in children and covers communication, gross motor, fine motor, problem-solving, and personal adaptive skills.

The authors compared 799 of the women who received the vaccine with 426 who did not. They found no association with negative developmental effects after controlling for factors such as flu status during pregnancy, high-risk medical conditions, and maternal vaccination before pregnancy.

“These findings fill a gap in the evidence base on the longer-term impact of influenza vaccination in pregnancy on child development,” Avalos said. The results were also strengthened by the large sample of diverse patients from two large geographic areas, she added.

The study was a secondary analysis of data from the 2010-2011 Pregnancy and Influenza Project (PIP), a multi-site prospective cohort study of members of Kaiser Permanente’s Northern California and Northwest regions funded by the Centers for Disease Control and Prevention (CDC) to assess the impact of influenza and influenza vaccine effectiveness in pregnant women and their infants. Avalos and colleagues explored the impact of influenza vaccination during pregnancy on the development of the infant.

“This study adds to the substantial and growing evidence base that pregnant women do not need to be concerned about the safety of the flu shot,” Avalos said.

Flu can result in severe complications and adverse pregnancy outcomes including stillbirth and preterm delivery. Women with influenza are twice as likely to be hospitalized if they are pregnant, the CDC reports. Nevertheless, the CDC found only about half (54%) of pregnant women received a flu shot during the 2018-2019 flu season.

The women in this study received the trivalent inactivated influenza vaccine (IIV3), as pregnant women are advised not to take the “live attenuated” version that is given as a nasal spray.

The study was funded by the Centers for Disease Control and Prevention and the National Institute of Mental Health.

Coauthors were De-Kun Li, MD, PhD, Ousseny Zerbo, PhD, Jeannette Ferber, MPH, and Roxana Odouli, MSPH, of the Kaiser Permanente Northern California Division of Research; Allison L. Naleway, PhD, Joanna Bulkley, PhD, and Tia L. Kauffman, MPH, of the Kaiser Permanente Northwest Center for Health Research; Sarah Ball, PhD, MPH, and Pat Shifflett, RN, MS, of Abt Associates; and Mark Thompson, PhD, Janet Cragan, MD, and Jennifer Williams, PhD, MSN, MPH, FNC-BC, of the Centers for Disease Control and Prevention.

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