Maternal influenza vaccination during pregnancy protects infants

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A recent study found that vaccination of pregnant mothers against influenza prevents young infants from being hospitalized with influenza.

Influenza vaccination has been proven effective in preventing influenza in pregnant women. Maternal vaccination may also protect the infant because maternal antibodies can cross the placenta and protect the infant at birth. There is no influenza her vaccine approved for infants under 6 months of age, so maternal vaccination may be a valuable protective measure.

Although the incidence of influenza-related hospitalizations is low and difficult to monitor, data from observational studies show that influenza-related hospitalizations in infants are reduced after maternal vaccination during pregnancy.

To understand how influenza vaccination during pregnancy affects severe influenza in infants, researchers conducted a prospective test-negative study. The primary outcome of this study was a reduction in influenza confirmed by polymerase chain reaction (PCR) during the first 6 months of life.

Immunization was provided to two cities in South Africa to increase maternal vaccination among women attending selected antenatal clinics. Her IIV formulation, trivalent, was the only vaccine available against influenza during the testing period.

Infants younger than 6 months of age received active active surveillance if they were hospitalized for acute respiratory illness or febrile illness. Pregnant women and women within 42 days of giving birth were also monitored if she was hospitalized with cardiopulmonary disease during any of the four influenza seasons in which the study was conducted.

Respiratory swabs were collected from participants and analyzed by real-time influenza PCR. Information from the prenatal card was used to determine maternal vaccination status. For a woman to be considered vaccinated, written documentation of her IIV vaccination was required during pregnancy and at least 14 weeks before her birth.

Of the infants included in the analysis, 71 were positive for influenza and 371 were negative. 26.8% of infants with positive test results had their mothers vaccinated against influenza during pregnancy, while 35.6% of infants with negative test results had their mothers vaccinated.

28.6% of influenza-positive women were vaccinated and 38.3% of influenza-negative women were vaccinated. These results indicated that the vaccine was effective in preventing influenza in mothers who infected their infants when vaccination was given during pregnancy.


Nunes MC, Walaza S, Meiring S, Zar HJ, Reubenson G, McMorrow M, et al. Effectiveness of maternal influenza vaccination for the prevention of influenza-related hospitalization in pregnant women and premature infants in South Africa: a prospective negative study. open forum infections2022;9(11).doi:10.1093/ofid/ofac552

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