Prenatal Flu Vaccine Not Linked to Adverse Early Childhood Outcomes

By Lisa Rapaport

August 05, 2020

(Reuters Health) - In utero exposure to influenza vaccines doesn't appear to contribute to mortality, morbidity or adverse health outcomes in children under five years of age, a systematic review suggests.

Researchers identified 3,647 studies done between 1980 and 2012, nine of which met the inclusion criteria: mother-child pairs with reported in utero exposure to influenza vaccines, an unexposed mother-child pair control group, and at least one health outcome investigated in children aged 6 months to five years.

The studies examined influenza infections and other infectious outcomes, as well as morbidity and mortality and outcomes related to atopic, autoimmune, and neurodevelopmental conditions. The researchers didn't find associations between in utero influenza vaccine exposure and any outcomes; they lacked sufficient data to perform a meta-analysis.

"Based on the results of our review, we feel the published research supports the long-term safety of vaccination during pregnancy," said lead study author Damien Foo of the School of Public Health at Curtin University in Perth, Australia.

"This should be reassuring for pregnant women who may be considering vaccination but are concerned about possible long-term side effects of vaccination during pregnancy, and this should also reassure clinicians who recommend vaccines to pregnant women," Foo said by email.

In two studies that looked at influenza infection, there wasn't a difference in infection rates for infants up to 6 or 12 months old based on whether they had in utero exposure to influenza vaccination.

Two studies in primary care settings that assessed infections such as common colds, pharyngitis, otitis, pneumonia, and gastrointestinal infections also found no differences between children exposed to the influenza vaccine in utero and unexposed children.

Studies that looked at respiratory infections found a lower risk of upper respiratory tract infections (adjusted rate ratio 0.92) but not lower respiratory tract infections in children exposed to the influenza vaccine in utero.

In addition, researchers found no differences in rates of asthma or autism between kids exposed to the influenza vaccine in utero and unexposed children. There were also no significant associations for celiac disease, Crohn disease, ulcerative colitis, juvenile arthritis, vasculitis, reactive arthropathy, idiopathic thrombocytopenic purpura, idiopathic urticaria, type 1 diabetes, Bell palsy, epilepsy, Guillain-Barre syndrome, intellectual disability, neoplasms, and sensory disorders.

Four of the studies in the analysis had a moderate to high risk of bias, the study team notes in Pediatrics. Another limitation of the analysis was the lack of sufficient data to assess risk based on trimester or gestational age.

In addition, the smaller studies in the analysis used different methods to determine exposure to the vaccine or any resulting health outcomes, and looked at a variety of types of vaccines including seasonal, pandemic, adjuvated, nonadjuvanted, monovalent, and trivalent.

Still, clinicians and pregnant women should be reassured by the findings that influenza vaccination is safe during pregnancy, said Dr. Flor Munoz, an associate professor of pediatrics and infectious diseases at Baylor College of Medicine and Texas Children's Hospital in Houston.

"There are no changes to clinical care based on these findings," Dr. Munoz, co-author of an editorial accompanying the study, said by email. "One hopes that the clinical change is that more women are vaccinated because of these findings."

SOURCE: and Pediatrics, online July 31, 2020.