President Obama released his $4 trillion fiscal year 2016 budget proposal Monday, and in it he outlined some ambitious health care initiatives to improve efficiency and eliminate waste. But buried a little bit deeper is a $50 million cut to one of the U.S.’s longstanding vaccine programs for the under- and un-insured.

The fiscal 2016 budget includes $561 million for the Health and Human Service’s 317 immunization program, a decrease from the current $611 million allotted to the initiative.

The defunding comes amid a severe measles outbreak that has officials at the Centers for Disease Control and Prevention (CDC) worried about how it may spread. At least 102 people have been infected by the airborne disease, raising a renewed debate over mandatory vaccinations, as well as the importance of adult immunizations.

The 317 immunization program aims to provide vaccines at no cost to eligible adults. The program has existed for over 50 years and plays a critical role in achieving national immunization coverage targets. It aims to protect public health by ensuring that under-insured populations receive the necessary vaccinations, from measles-mumps-rubella to the seasonal flu vaccines.

Officials believe that health insurance expansion will further increase access to immunizations and decrease the number of people who need Section 317 vaccinations.

However, even with the roll-out of the Affordable Care Act, the number of uninsured Americans is at near-historic low, with 11.3% still without insurance as of the second quarter of last year, according the National Center for Health Statistics.

The cut in the immunization program only affects immunization access for under- and un-insured adults; the Vaccines for Children initiative is safe. The 2016 budget includes an increase of $128.1 million in mandatory funding for the program, which provides vaccines at no charge to children under 19-years-old.

The White House did not respond to a request for comment on this story.