Thursday, March 31, 2016

Clinical Infectious Diseases: Flu Vaccine May Reduce Incidence of Stillbirth

Credit CDC


We’ve known for a long time that influenza during pregnancy can endanger both the the mother and unborn child. During the 2009 H1N1 pandemic pregnant women were six times more likely to be hospitalized than non-pregnant women (see Pregnancy & Flu: A Bad Combination).

Worse, in 2011's  BMJ: Perinatal Outcomes After Maternal 2009 H1N1 Infection we saw a study showing women who were admitted to the hospital with maternal H1N1 infection experienced a 3 to 4 times higher rate of preterm birth, 4 to 5 times greater risk of stillbirth, and a 4 to 6 times higher rate of neonatal death.

Despite these sobering outcomes, many women forgo flu vaccines out of concern over their safety during pregnancy.  The science, however, overwhelmingly supports the safety of flu shots for pregnant women.

We've another study, published last night in the journal Clinical Infectious Diseases, that strongly suggests influenza vaccination during pregnancy can substantially reduce the rate of stillbirth.

First a link and some excerpts from the study, followed by some excerpts from the IDSA press release.

Seasonal Trivalent Influenza Vaccination During Pregnancy and the Incidence of Stillbirth: Population-Based Retrospective Cohort Study


Background.  Although antenatal influenza vaccination is an important public health intervention for preventing serious infection in pregnant women and newborns, reported vaccine coverage is often less than 50%. Concern for the safety to the fetus is a commonly cited reason for vaccine hesitancy and refusal. The incidence of stillbirth following pandemic vaccination has been previously studied; however, no population-based study has evaluated the incidence of stillbirth following seasonal trivalent influenza vaccination.

Conclusions.  Mothers who received seasonal TIV during pregnancy were significantly less likely to experience stillbirth compared with unvaccinated mothers. These results support the safety of seasonal influenza immunization during pregnancy and suggest a protective effect.

Public Release: 
 Infectious Diseases Society of America
Seasonal influenza vaccination may guard against stillbirth, a new study published in Clinical Infectious Diseases and available online suggests. Researchers in Western Australia analyzed data from nearly 60,000 births that occurred during the southern hemisphere's 2012 and 2013 seasonal influenza epidemics, and found that women who received the trivalent influenza vaccine during pregnancy were 51 percent less likely to experience a stillbirth than unvaccinated mothers. 

The retrospective study used midwives' records to examine a cohort of 58,008 births: 52,932 to mothers who had not received the vaccine and 5,076 to mothers who had been vaccinated during pregnancy. All births took place in Western Australia between April of 2012 and December of 2013. The adjusted risk of stillbirth among vaccinated mothers was 51 percent lower than the risk among women who had not been vaccinated.

Researchers also observed that stillbirth rates increased after periods of influenza virus circulation and decreased during the months prior to the influenza season, although the seasonal differences were not statistically significant. The study's results are consistent with those of a 2000 study in Switzerland that recorded increased incidence of stillbirth in relation to the northern hemisphere's influenza season, as well as with similar research conducted during the influenza A/H1N1 pandemic. 

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