A review of more than 1,000 hospitalizations revealed a 40% influenza vaccine effectiveness against laboratory-confirmed influenza-associated hospitalizations during pregnancy, Mark Thompson, MD, said at a meeting of the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices in Atlanta.
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To date, no study has examined influenza vaccine effectiveness (IVE) against hospitalizations among pregnant women, said Dr. Thompson, of the CDC’s influenza division.
He presented results of a study based on data from the Pregnancy Influenza Vaccine Effectiveness Network (PREVENT), which included public health or health care systems with integrated laboratory, medical, and vaccination records in Australia, Canada (Alberta and Ontario), Israel, and three states (California, Oregon, and Washington). The study included women aged 18-50 years who were pregnant during local influenza seasons from 2010 to 2016. Most of the women were older than 35 years (79%), and in the third trimester (65%), and had no high risk medical conditions (66%). The study was published in Clinical Infectious Diseases (2018 Oct 11. doi: 10.1093/cid/ciy737).
The researchers identified 19,450 hospitalizations with an acute respiratory or febrile illness discharge diagnosis and clinician-ordered real-time reverse transcription polymerase chain reaction (rRT-PCR) testing for flu viruses. Of these, 1,030 (6%) of the women underwent rRT-PCR testing, 54% were diagnosed with either influenza or pneumonia, and 58% had detectable influenza A or B virus infections.
Overall, the adjusted IVE was 40%; 13% of rRT-PCR-confirmed influenza-positive pregnant women and 22% of influenza-negative pregnant women were vaccinated; IVE was adjusted for site, season, season timing, and high-risk medical conditions.
“The takeaway is this is the average performance of the vaccine across multiple countries and different seasons,” and the vaccine effectiveness appeared stable across high-risk medical conditions and trimesters of pregnancy, Dr. Thompson said.
The generalizability of the study findings was limited by the lack of data from low- to middle-income countries, he said during the meeting discussion. However, the ICU admission rate is “what we would expect” and similar to results from previous studies. The consistent results showed the need to increase flu vaccination for pregnant women worldwide and to include study populations from lower-income countries in future research.
Dr. Thompson had no financial conflicts to disclose.