It's the county's first reported measles case since 2024.
The Nassau County Department of Health says it's working with the New York State Department of Health to investigate how the child was exposed and to prevent the virus from spreading further.
"The Nassau County Department of Health is closely investigating the case, including any potential exposures, and taking the necessary steps to prevent the spread of measles," said Health Commissioner Dr. Irina Gelman.
She warned that measles can be serious, sometimes leading to pneumonia, brain inflammation or hospitalization, and urged families to make sure vaccinations are up to date.
Measles spreads easily through the air when an infected person coughs or sneezes, or by touching contaminated surfaces and then touching the face.
Symptoms usually start with fever, cough, runny nose and watery eyes, followed by a rash several days later. Someone with measles can spread the virus both before and after the rash appears.
Health officials say anyone who may have been exposed and is feeling sick should call their doctor or medical facility before going in, so steps can be taken to avoid exposing others.
Doctors say vaccination is the best protection. Two doses of the MMR vaccine provide strong immunity, and the vaccine is considered very safe. Anyone unsure of their vaccination status is encouraged to check with their health care provider.
According to the New York State Department of Health, so far in 2026, there have been five confirmed cases of measles in New York City and five in New York State outside of NYC for 10 total.
In 2025, there were 20 confirmed cases in New York City and 28 in New York State outside of NYC for 48 total.
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