UM Researchers Find 1 in 6 Toddlers Don’t Finish Multidose Vaccine Series

UM researchers Alexandria Albers, Dr. Sophia Newcomer and Sarah Michels. (L-R)

MISSOULA – University of Montana researchers have found that 17% of U.S. toddlers start, but do not complete, common and recommended vaccine series.

UM’s Alexandria Albers, Sarah Michels and Sophia Newcomer published their findings in Pediatrics this summer, highlighting the primary cause of not completing a vaccine series is due to logistical barriers and not vaccine hesitancy. When publishing the study, the researchers urged action to address this public health shortcoming.

“For most vaccines, children need three or four doses in the first two years of life for optimal protection against diseases that can be quite dangerous,” said  Michels, an epidemiology specialist with the UM Center for Population Health Research and lead author of the study. “Completing all doses of multidose vaccine series is important for long-lasting immunity.”

The researchers analyzed data collected in the CDC’s National Immunization Survey from 16,365 children ages 19 to 35 months. In addition to finding that 17% of U.S. children started but did not finish their vaccine series, the researchers found that 10% did not start one or more vaccine series, including 1% of toddlers who did not receive any vaccines. About 73% of toddlers did complete all seven recommended vaccine series analyzed in the study.

The vaccines the researchers specifically evaluated were four doses of diphtheria, tetanus and acellular pertussis; four doses of pneumococcal conjugate; three or four doses of Haemophilus influenzae type b; three doses of hepatitis B; three doses of polio; one dose of measles, mumps and rubella; and one dose of varicella vaccines.

The researchers found that children who moved across state lines, children who did not have health insurance and families with multiple children in the household, were more likely to have started, but not completed, multidose vaccine series. Socioeconomic and racial and ethnic disparities were also observed, which indicate that effective strategies for supporting vaccine series completion are not reaching all communities.

“Concerted efforts are needed to close these gaps,” said  Newcomer, an associate professor of epidemiology at UM and the study’s senior author. “Clinics can proactively reach out to families to let them know when their kids are due for vaccines, offer flexible scheduling and appointment options, and make sure eligible children are getting free vaccines through the federal Vaccines for Children program. We need to make getting vaccinated as easy as possible.”

The study was led by UM researchers through a collaboration with the UM Center for Population Health Research, Yale School of Public Health and Kaiser Permanente.

“Having the opportunity to work within a national research collaboration has been a significant learning experience for me,” said Albers, a UM Public Health Ph.D. student who was a co-author of the study. “Our study’s results offer insight into how we can more effectively deliver immunization services to children across the country.”


Contact: Dr. Sophia Newcomer, associate professor of epidemiology, UM School of Public and Community Health Sciences 406-243-4745,; Sarah Michels, UM Center for Population Health Research epidemiology specialist,; Alexandria Albers, UM Public Health Ph.D. student,