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Study identifies geographic clusters of pregnant women who missed flu shots

Women with fewer prenatal visits less likely to get vaccinated while pregnant, Kaiser Permanente research finds.

A Kaiser Permanente analysis of women who did not get flu shots during their pregnancies found the women clustered in geographic “hot spots.” These women tended to have fewer prenatal medical visits and live in low-income neighborhoods.

The findings suggest a socioeconomic connection with being unvaccinated for influenza, said study lead author Ousseny Zerbo, PhD, a research scientist with the Kaiser Permanente Division of Research. “This study contributes to the growing body of evidence associating health status with where people live, and the socioeconomic conditions they live in,” Zerbo said.

Ousseny Zerbo, PhD, research scientist, Kaiser Permanente Vaccine Study Center

He also noted a contrast with clusters of people who choose not to vaccinate their children. “Unlike childhood under-vaccination, which clusters in high socioeconomic neighborhoods, skipping the influenza vaccine clusters in low-income neighborhoods,” Zerbo said.

The women who did not get a flu shot were more likely to be Black or Hispanic and have subsidized health insurance. The study was not able to identify reasons why these women did not get the flu vaccine. But Zerbo said economics could be a factor and suggested efforts by health care providers to bring flu shot clinics to low-income neighborhoods might increase flu vaccination rates.

The study was published recently online in the American Journal of Epidemiology.

Getting the flu during pregnancy can result in severe complications and adverse pregnancy outcomes including stillbirth and preterm delivery. The Centers for Disease Control and Prevention (CDC) recommends all pregnant women get the flu vaccine regardless of how far along they are in their pregnancy.

In this study of 77,607 pregnant members of Kaiser Permanente Northern California, 53% did not get a flu shot in 2015 or 2016, similar to the national rate found by the CDC in the 2018-2019 flu season.

The study found hot spots of unvaccinated pregnant women in Fresno, Roseville, Napa/Sonoma, East Oakland, and South East San Jose. Within these geographic clusters, unvaccinated rates ranged from 57% to 75%. The cluster in Fresno, with a 42% increased risk of being unvaccinated compared with living outside a cluster, had the highest rate of unvaccinated pregnant women (75%).

The strongest demographic factors associated with not being vaccinated were being Black or Hispanic, being age 41-45, not having had a previous flu shot, and not having an initial prenatal visit in the first trimester. Median family income was not strongly associated with being unvaccinated, but there was an increased likelihood among women living in neighborhoods with a high deprivation index, a measure that includes the proportion of residents who are low income, have a low education level, and are unemployed.

Nicola Klein, MD, PhD, director, Vaccine Study Center.

The authors noted women with these socioeconomic factors may have logistical barriers to vaccination, such as lack of transportation or time off work. They suggested clinicians should recommend flu shots early to these women because they may not be able to attend as many prenatal visits as women in other economic circumstances.

The authors also suggested women who do not get a flu shot may not be aware of the benefits of the vaccine or believe the vaccine might be harmful to their baby. “These findings can help health care providers identify pregnant women who may have concerns and reassure them that safety of these vaccines has been well studied and they are safe for both mother and child,” said senior author Nicola Klein, MD, PhD, director of the Kaiser Permanente Vaccine Study Center.

Multiple studies, including some by the Kaiser Permanente researchers, have explored potential associations between influenza vaccines and autism or developmental problems in children and found no increased risk. Getting vaccinated reduced the chance a pregnant woman would be hospitalized for flu by 40% in a 2018 Kaiser Permanente study. Vaccination of the mother during pregnancy may also protect infants during their first 6 months, before they can be vaccinated.

The study highlights the value of clinicians understanding women’s voices around vaccination and discussing the benefits of the vaccine for all mothers and babies, said Kari Carlson, MD, director of women’s health for The Permanente Medical Group. Accessibility to vaccination is also important, she said. “Our outreach into communities – as well as drive-up and walk-up clinics with variable hours – can provide more opportunities for patients to receive vaccinations.”

Carlson noted the particular importance this year of controlling the spread of influenza through vaccination to avoid compounding a possible COVID-19 infection with flu. “Kaiser Permanente is committed to vaccinating our pregnant community and preventing serious illnesses,” she said.

The study was funded by the National Institute of Allergy and Infectious Diseases.

Coauthors included Thomas Ray, MBA, Lea Zhang, Kristin Goddard, MPH, Bruce Fireman, MA, and Alyce Adams, PhD, of the Division of Research; Saad Omer, MPH, PhD, of Yale University; and Martin Kulldorff, PhD, of Harvard Medical School.

About the Kaiser Permanente Division of Research  

The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 450 epidemiological and health services research projects. For more information, visit or follow us @KPDOR. 





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