Seasonal influenza vaccination during pregnancy reduces stillbirths

Issue: May 2016

Women who received seasonal trivalent influenza vaccine during pregnancy were 51% less likely to experience stillbirth than those who did not receive the immunization, according to a study recently published in Clinical Infectious Diseases.

“Pregnant women trust and rely on their health care providers to advise them during their pregnancy. In fact, 80% of pregnant women say they would get vaccinated had their health care provider recommended it to them,” Annette K. Regan, MPH, of the University of Western Australia, Crawley, and the Western Australia Department of Health, told Infectious Disease News. “Stillbirth is a devastating loss for any parent, and these results show that clinicians treating pregnant women should be promoting seasonal influenza vaccine every year for every pregnancy.”

Annette K. Regan

Reduction in stillbirths more pronounced after flu season

To examine the relationship between influenza vaccination and neonatal outcomes, Regan and colleagues analyzed data from 58,008 mothers who delivered in Western Australia from April 2012 through December 2013. Women with a dated vaccination record in the Western Australia Antenatal Influenza Vaccination Database occurring between the estimated date of conception and 14 days before delivery were considered to be vaccinated during pregnancy. Incidence of stillbirth — defined as a birth with an Apgar score of zero at 1 and 5 minutes after birth along with stillborn status recorded by a clinician — was determined using data from the Midwives Notification System, as were maternal characteristics such as age, pre-existing medical conditions or pregnancy complications. These factors and outcomes were analyzed to determine the risk for stillbirth during the pre-influenza season, influenza season and post-influenza season time periods.

The final analysis consisted of 5,076 vaccinated mothers and 52,932 unvaccinated mothers, which translated to an 8.7% pregnancy immunization rate. Four-fifths of all births were among mothers aged younger than 35 years, 94% were among nonindigenous persons, 44% occurred among metropolitan residents, and 65% were determined to be women in the top 20% of socioeconomic level. Vaccination was significantly more frequent among women aged older than 35 years, women with pre-existing medical conditions, women in the highest socioeconomic level and women residing in areas considered highly accessible.

There were 377 stillbirths observed during the study period — a rate of 6.5 stillbirths per 1,000 births. The unadjusted rate of stillbirths per 100,000 pregnancy days was five for unvaccinated women and three for vaccinated women. In an adjusted analysis, stillbirths were 51% less likely to occur among vaccinated vs. unvaccinated women (adjusted HR = 0.49; 95% CI, 0.29-0.84), a reduction that was more pronounced when limiting the analysis to births occurring during the post-influenza season time period (adjusted HR = 0.33; 95% CI, 0.12-0.88). Other observed trends included associations between stillbirth and diabetes, hypertension, smoking and a nonsingleton pregnancy.

These findings are consistent with previous data, which suggested that maternal influenza vaccination could reduce stillbirths during an influenza pandemic, the researchers wrote. However, Regan said additional studies are necessary to examine the impact of other complicating factors and scenarios.

“To date, there have been no studies that have looked at how well this reduction persists when the seasonal vaccine poorly matches the circulating virus types,” Regan said. “Given that stillbirth is a relatively uncommon pregnancy complication in developed countries, we need very large sample sizes each year to look at this more closely.”

Many providers do not adhere to vaccination recommendations

Previous data have suggested that influenza vaccination during pregnancy could reduce the risk for negative neonatal outcomes such as preterm birth and low birth weight. As such, current guidelines for vaccination in the U.S. and Canada recommend that all pregnant women receive the influenza vaccine.

Michael Desjardins

Despite this, evidence presented by Michael Desjardins, PhD, from the Montreal University Health Centre, and colleagues at ICAAC 2015 indicate that approximately 40% of Québécois providers did not offer the vaccine to pregnant women in their care.

In their study, the researchers administered an online survey to nearly 350 health care providers who followed at least one pregnant woman within the past year. Respondents were considered to be adherent if they reported offering the vaccine to at least 75% of pregnant patients.

Approximately 60% of the participants were compliant with either Canadian (49%) or Quebec (51%) vaccination guidelines, according to Desjardins and colleagues. Providers who were aged younger than 40 years, did not have an academic practice or reported lower follow-up rates per year were all less likely to offer the vaccine. Adherence rates varied among professions, with obstetricians-gynecologists most commonly reporting vaccine recommendations (80%) while midwives did so rarely (12%).

“Population as well as health care providers must be informed of the clear benefits associated with influenza vaccine and its safety during pregnancy,” Desjardins said. “Actions should rapidly be taken to improve vaccination coverage in this high-risk population.” – by Dave Muoio

References:

Desjardins M, et al. Abstract I-298. Presented at: Interscience Conference on Antimicrobial Agents and Chemotherapy; Sept. 17-21, 2015; San Diego.

Regan AK, et al. Clin Infect Dis. 2016;doi:10.1093/cid/ciw082.

Disclosure: The researchers report no relevant financial disclosures.