October 12, 2018
2 min read

Vaccination reduces flu-related hospitalization risk in pregnant women by 40%

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Vaccination reduced the risk that pregnant women would experience influenza-related hospitalization by 40% during six recent influenza seasons, according to results from a multinational study published in Clinical Infectious Diseases.

“Expecting mothers face a number of threats to their health and the health of their baby during pregnancy, and getting the flu is one of them,” Allison L. Naleway, PhD, senior investigator and associate director of science programs in the Kaiser Permanente Center for Health Research, said in a news release. “This study’s findings underscore the fact that there is a simple, yet impactful way to reduce the possibility of complications from flu during pregnancy: get a flu shot.”

Researchers from the CDC and other public health agencies and universities in the United States, Australia, Canada and Israel collaborated on the study through the Pregnancy Influenza Vaccine Effectiveness Network, which comprises five study sites in the four countries. The sites reviewed records of pregnant women aged 18 to 50 years with pregnancies that overlapped with influenza seasons between 2010 and 2016. Naleway and colleagues used administrative data to identify hospitalized patients with acute respiratory or febrile illness (ARFI) and real-time RT-PCR (rRT-PCR) tests for influenza that were ordered by clinicians.

According to the study findings, 84% (n = 1.72 million) of the pregnancies overlapped with an influenza season. The researchers identified 19,450 hospitalizations for ARFI, including just 6% (n = 1,030) who were tested for influenza viruses using rRT-PCR. Fifty-four percent of the women had pneumonia or influenza discharge diagnoses. Testing detected influenza A or B virus infection in 58% (n = 598) of the women hospitalized with ARFI. Women who were aged younger than 35 years (79%), were in their third trimester (65%) and had no high-risk medical conditions (66%) accounted for most of the ARFI hospitalizations.

pregnant woman recieiving flu shot 
Influenza vaccination was 40% effective in pregnant women during six recent influenza seasons.
Source: Adobe Stock

Study findings showed that 13% of pregnant women with rRT-PCR-confirmed influenza had been vaccinated, compared with 22% of women who tested negative for influenza, for an adjusted influenza vaccine effectiveness of 40% (95% CI, 12%-59%) against influenza-associated hospitalization in pregnant women, the researchers reported.

“Our study found that flu vaccination worked equally well for women in any trimester and even reduced the risk of being sick with influenza during delivery,” Mark Thomson, PhD, an epidemiologist in the CDC’s Influenza Division, said in the release. – by Bruce Thiel

Disclosures: Naleway reports receiving grants from Pfizer, MedImmune/Astra Zeneca and Merck outside the submitted work. Thompson reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.