Offspring of women who receive influenza immunisation during pregnancy have better intrauterine growth and fewer respiratory illnesses during flu season, according to a new study.
"Influenza immunisation during pregnancy protects the mother, the baby on board, and the infant from 0 to 6 months," lead author Dr Mark C. Steinhoff told Reuters Health by email.
"Given that there is substantial data regarding the safety of influenza immunisation in pregnancy, physicians should encourage the use of this three-for-one intervention," added Dr Steinhoff, of Cincinnati Children's Hospital Medical Centre in Ohio.
The findings were published online in CMAJ.
Respiratory illness lower in flu vaccination group
Dr Steinhoff and colleagues conducted a secondary analysis of data from the Mother’s Gift project in Bangladesh to see if influenza immunisation affects infants whose mothers were exposed to influenza during pregnancy.
The study included 172 pregnant women who received inactivated influenza vaccine and 168 pregnant women who received pneumococcal vaccine (control). Three hundred twenty-seven of their infants were included in the analysis.
During the entire study period, there were significantly fewer infants who were small for gestational age in the influenza vaccination group than in the control group (28% vs. 38%; p=0.05); and the overall mean birth weight was 3% higher in the influenza vaccine group than in the control group (p=0.09).
During the period with circulating influenza virus, the incidence of maternal plus infant respiratory illness was 49% lower in the influenza vaccination group than in the control group (p=0.0003). The proportion of infants who were small for gestational age was 57% lower in the influenza vaccination group than in the control group (25.9% vs. 44.8%; p=0.03).
Flu vaccine has no influence
In contrast, during the time with limited influenza virus circulation, influenza vaccine had no apparent impact on maternal plus infant respiratory illness or on the proportion of infants who were small for gestational age.
Mean birth weights were significantly higher in the influenza vaccine group, but only during the period with circulating influenza virus.
Gestational age at birth, Apgar scores, and maternal age, parity, height, and postpartum weight did not differ between the groups in multiple logistic regression analysis.
Pregnant women reluctant to receive immunisation
"People often ask if these data from Bangladesh are generalisable," Dr Steinhoff said. "I have noted that there are four publications in 2011, all retrospective studies either of women who received vaccine, compared to those who did not, or of women ill during flu season or with proven flu illness compared to those who had not.
All four show a significant increase in mean birth weights ranging from 90g to 285g. To summarise, the results from our study were unique and not previously published, but four studies have now shown the effect of influenza in pregnancy is probably real."
Dr Steinhoff added, "My obstetric colleagues tell me that while pregnant women may be reluctant to receive immunisations, the data that it will protect them from illness, improve the growth of the baby on board, and prevent influenza illness in the infant provide them with the full information regarding the benefits of immunisation. There are several recent economic analyses of antenatal maternal influenza immunisation, all of which show that it are cost-saving."
(Will Boggs, Reuters Health, February 2012)
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