The outbreak has resulted in nearly 500 cases in Texas, and has spread across 22 states.
The unvaccinated school-aged child, who had no underlying health conditions, died on Thursday (local time) in the hospital from measles pulmonary failure, the Texas Department of State Health Services said.
"The child was receiving treatment for complications of measles while hospitalized," Aaron Davis, a spokesperson for UMC Health System in Lubbock, Texas, said in an email.
It is the second death of a child in Texas since the measles outbreak began in late January in Gaines County, where the vaccination rate is about 82%, below the 95% considered protective for those who cannot be vaccinated.
When asked about the measles death, US President Donald Trump told reporters on Air Force One that if the outbreak progresses his administration will "have to take action very strongly."
Health and Human Services Secretary Robert F Kennedy Jr, in a post on X, identified the child as 8-year-old Daisy Hildebrand and said he visited Texas on Sunday to comfort the family.
Kennedy, an anti-vaccine advocate who has declared that vaccination is a personal choice, said on Sunday vaccines are the best protection against measles.
"The most effective way to prevent the spread of measles is the MMR vaccine," he said in the post on X. He said that as of Sunday there were 642 confirmed cases of measles, 499 of those in Texas.
Kennedy has previously also recommended Vitamin A as a measles treatment, along with good nutrition. While Vitamin A has been shown in some studies in developing countries to lessen the severity of symptoms, it can lead to liver toxicity in high quantities.
Republican US Senator Bill Cassidy, a physician who chairs the Senate health committee, wrote on X after the child's death was disclosed: "Everyone should be vaccinated."
"Top health officials should say so unequivocally b/4 another child dies," Cassidy wrote on X.
Cassidy had backed Kennedy's confirmation after Kennedy promised not to make changes to vaccine oversight.
The measles vaccine is 97% effective after two shots.
He said teams from the US Centers for Disease Control and Prevention have been redeployed to Texas at the request of the state's governor, Greg Abbott.
The CDC on its website says the vaccine is "the best protection against measles," which spreads through the air when an infected person sneezes or coughs.
KENNEDY HEARING POSTPONED
Cassidy last week called for Kennedy to appear before the Senate health committee on April 10 to discuss the US health department's restructuring in which 10,000 people were being laid off, including from the Food and Drug Administration and the Centers for Disease Control and Prevention.
But on Friday a committee official said the hearing would not occur on April 10 because seven days' notice had not been given as required by committee procedure. No date has been set.
The Texas Department of State Health Services reportedon Friday 59 new measles cases in three days, a 15% jump, for a total of 481 in the state since late January.
Related measles outbreaks have been reported in other states, including New Mexico and Oklahoma. In addition, an unvaccinated New Mexico adult tested positive for measles after dying in March.
As of Thursday, the Centers for Disease Control and Prevention reported a weekly nationwide increase of 124 measles cases, bringing the total to 607 so far this year. That compares to a nationwide total in 2024 of 285 reported cases.
CDC officials said 97% of US cases are unvaccinated or have an unknown vaccination status.
Pediatricians and other doctors are pushing back against vaccine hesitancy and warning parents that vitamin A and other supplements touted by vaccine critics will not protect their children from the highly contagious and potentially fatal disease.
