Vaccination Lowers Risk for Adverse Birth Outcomes During Influenza Season

In women who are hospitalized for an acute respiratory infection (ARI) during the influenza season, being pregnant is a risk factor for adverse birth outcomes, and influenza vaccination reduces this risk, according to study findings published in Influenza and Other Respiratory Viruses.

Recognizing that influenza vaccination coverage in the Western Pacific Region remains low, researchers in New Zealand sought to provide additional data for this locale regarding the effect of maternal influenza immunization on birth outcomes. The investigators conducted a 16-year, retrospective, population-based cohort study involving female residents of New Zealand of reproductive age (ie, 15 to 49 years) who were pregnant at any time between January 1, 2003, and December 31, 2018. A total of 822,391 pregnancies among New Zealand residents of reproductive age were identified during the 16-year study period. The average patient age was 29 years (median age, 30 years; range, 25 to 34 years).

Results of the study showed that overall, 0.6% (5095 of 822,391) pregnant women had at least 1 ARI hospitalization during the influenza season (ie, May through September). Moreover, the pregnancies of these women were at a greater risk for preterm birth (adjusted hazard ratio [aHR], 1.50; 95% CI, 1.39-1.61) and low birth weight (aHR, 1.64; 95% CI, 1.51-1.79) compared with pregnancies without such hospitalizations. No association was reported, however, between maternal hospitalization for ARI and fetal death (aHR, 0.96; 95% CI, 0.69 to 1.34) during the influenza season.

Maternal influenza vaccination during pregnancy was associated with a lower risk for fetal death (incidence rate, 1.0 vs 1.9 per 10,000 person-weeks; aHR, 0.50; 95% CI, 0.44-0.57), preterm birth (incidence rate, 15.5 vs 20.3; aHR, 0.79; 95% CI, 0.77-0.82), and low birth weight (incidence rate, 1.1 vs 1.3; aHR, 0.87; 95% CI, 0.83-0.90).

Limitations of the present study include: lack of inclusion of pregnant women with ARIs who sought care in ambulatory settings; the unexplored possibility that hospitalized pregnant women were more likely to have gestational diabetes as well as other underlying medical conditions that could affect their birth outcomes; the possibility that some maternal ARI hospitalizations analyzed were related to non-influenza respiratory pathogens circulating during the influenza season.

The authors concluded that “Improving understanding, access and provider recommendations relating to maternal influenza in New Zealand could prove useful in improving pregnancy and birth outcomes.”

Disclosure: One of the study authors has declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of the author’s disclosures.