Routine childhood and adolescent immunizations declined in Michigan between 2017 and 2023, particularly among counties with lower household income and higher uninsurance rates, a new study suggests.
For many key pediatric vaccines, completion rates dropped sharply during the COVID-19 pandemic and have not yet recovered, according to Michigan Medicine led findings in Pediatrics.
"Our findings show that progress towards increasing childhood and adolescent immunizations is stalling in Michigan, increasing the risk of vaccine-preventable diseases," said senior author Kao-Ping Chua, M.D., Ph.D., a pediatrician and researcher at University of Michigan Health C.S. Mott Children's Hospital and the director of the Susan B. Meister Child Health Evaluation and Research ( CHEAR ) Center.
Researchers analyzed county-level data from Michigan's immunization registry between 2017 and 2023. During the study period, completion rates of a recommended group of childhood immunizations among toddlers (including vaccines for pertussis, polio, and measles-mumps-rubella among others) fell from nearly 76% to 67%.
Meanwhile, completion rates of a recommended group of vaccinations among adolescents (including vaccines for meningitis, pertussis, and tetanus) declined from about 81% to 75%.
The study also assessed adolescent completion rates of the human papillomavirus (HPV) vaccination series – which can prevent several types of cancers, including cervical and throat cancer. Although completion rates rose modestly — from 35% to 42% for males and 43% to 45% for females — the increases were smaller than expected based on pre-pandemic trends, in part because the rate of increase slowed after the COVID-19 pandemic began.
"Our findings suggest that the pandemic interrupted the progress that was being made in increasing HPV vaccination rates in adolescents," Chua said.
The researchers examined trends in immunization completion rates by county socioeconomic factors, including income and insurance coverage. The decline in the completion rates of the recommended group of childhood and adolescent immunizations was greater in counties with lower income and higher uninsurance, while the increase in the rate of the male HPV vaccination series was slower.
"These changes often resulted in the creation of new gaps in immunization completion rates by county income or uninsurance rate or the widening of pre-existing gaps", said Chua, who notes that this is one of the first studies to examine recent changes in childhood and adolescent immunizations by county characteristics.
Vaccines have long been one of the most effective tools in public health. In 2019, childhood immunizations were estimated to prevent over 24 million cases of vaccine-preventable diseases nationwide. Yet in 2025, the U.S. reported its highest number of measles cases in 33 years — a disease that had been declared eliminated in the country in 2000.
Michigan also saw a spike in measles with more than a dozen cases reported in 2025 as well as pertussis (whooping cough), with 855 cases reported the same year, including 152 in children under two.
"Reversing the declines in childhood and adolescent immunizations is crucial to prevent further outbreaks of measles and pertussis, both in Michigan and in the U.S. more broadly," Chua said.
"To achieve this goal, broad-based efforts to increase immunization rates in all counties should be coupled with targeted efforts focused on counties with lower income and higher uninsurance rates."
