Researchers funded by the National Institutes of Health (NIH) have identified and mapped the first comprehensive group of human antibodies that target the measles virus, a breakthrough that could lay the groundwork for the development of the first antibody-based treatment for measles.

The findings come as measles cases continue to rise in the United States and globally. More than 470,000 measles cases were reported worldwide in 2024, and at least 72 outbreaks have been recorded in the United States since January 2025, according to a news release from NIH.

While vaccines remain highly effective at preventing measles, no safe and effective therapies have received regulatory approval in the United States. That leaves immunocompromised people, pregnant women and infants too young to be vaccinated with limited medical options.

"With measles cases increasing, we urgently need effective therapeutics to protect the most vulnerable," Jeffrey K. Taubenberger, M.D., Ph.D., acting director of NIH's National Institute of Allergy and Infectious Diseases, said in the release. "This research gives us a clear picture for the first time of the most promising targets for antibody-based medicines that could protect or treat people for whom measles vaccination is not an option."

The study was led by Dr. Erica Ollmann Saphire of the La Jolla Institute for Immunology. Researchers isolated memory B cells, which retain long-term immune memory from infections or vaccinations, from a donor who had received three measles vaccinations. From those cells, the team engineered and purified more than 100 human monoclonal antibodies, each designed to target a specific site on the measles virus.

Using cryo-electron microscopy, scientists created the first atomic-resolution structural maps showing human antibodies bound to measles virus proteins. The team identified nine distinct sites on the virus' two surface proteins, Hemagglutinin, or H, and Fusion, or F, that are targeted by the antibodies.

According to the NIH, the findings challenge a long-standing belief that immunity against measles is driven primarily by antibodies targeting the H protein, while antibodies against the F protein play only a minor role. Researchers found antibodies against both proteins can provide strong and independent protection.

One antibody targeting the F protein, known as 4F09, delivered the strongest protection in the study. Researchers said it reduced measles virus levels in the lungs of infected rats to undetectable levels by locking the F protein in place and preventing the virus from entering human cells.

The identified antibodies also target parts of the virus that remain nearly identical across all known measles strains circulating worldwide, suggesting the virus may be unable to mutate enough to evade the antibodies while still surviving, according to the release.

Researchers are now seeking partners to conduct the additional testing and research needed to develop the discovery into a treatment that could serve both as a rapid post-exposure preventive and as a therapy for infected patients.

More information about the NIH and its programs is available at www.nih.gov.