On Jan. 2, 2026, U.S. states will no longer be required to report how many children they vaccinate to the Centers for Medicare and Medicaid Services (CMS), according to a December 30 letter to state health officials.

As a measure of the quality of the care, states have been required to report the percentage of patients covered by Medicaid and the Children’s Health Insurance Plan who are immunized. About 40% of children are covered by Medicaid, a federal health program administered by states for people with low incomes, pregnant women, those with disabilities, and others. CHIP provides health insurance to children whose families do not qualify for Medicaid.

States may continue to provide the information voluntarily, according to the letter, “to allow CMS to maintain a longitudinal dataset while exploring alternative immunization measures.” In the future, however, CMS will explore “new vaccine measures that capture information about whether parents and families were informed about vaccine choices, vaccine safety and side effects, and alternative vaccine schedules,” according to the letter.

The change comes amid efforts by US Health and Human Services (HHS) Secretary Robert F. Kennedy Jr.’s efforts to restrict access to vaccines. The Trump administration in December issued a memo to HHS officials to alter the US child immunization schedule, which currently protects against 18 life-threatening diseases, to resemble that of Denmark, which protects children against 10 diseases.

Tracking childhood immunization data is important, because it can help researchers and policymakers identify trends and problems in vaccine access, said Joshua M. Sharfstein, MD, a professor at the Johns Hopkins Bloomberg School of Public Health. “If CMS makes this change, it will become harder to understand gaps in vaccination that leave communities exposed to outbreaks of serious and even deadly infectious diseases,” Sharfstein told CIDRAP News.