The Texas Department of State Health Services reported on Friday that it was aware of 90 cases diagnosed in the last month in the South Plains area, in the north-west part of the state. At least 77 of them were reported in children and teens under 17.

In New Mexico, officials said nine people had become sick in Lea County, along the state’s eastern border with Texas.

Measles is highly contagious and can be deadly. The outbreaks come amid a rise in US anti-vaccine sentiment, including towards the measles, mumps and rubella (MMR) jab that is typically given during childhood.

Health officials in Texas say their figures are likely to be an underestimate, as some parents may not report infections or may not realise their child has the disease.

“It is troubling, because this was completely preventable,” Dr Amesh Adalja, an infectious disease physician and senior scholar at Johns Hopkins University, told CBS News, the BBC’s US news partner.

“It’s the most contagious infectious disease known to humans,” he added.

Symptoms of the highly-infectious illness include fever, cough, runny nose, eye irritation and a rash.

A measles infection can have particularly devastating complications for pregnant women and young children, including pneumonia, neurological impairment, hearing loss and death.

Survivors are at risk of developing a degenerative brain and nervous system disease known as subacute sclerosing panencephalitis (SSPE).

Most US children receive two shots to protect against the illness, which together are 97% effective in protecting against measles, according to the Centers for Disease Control and Prevention (CDC).

Health experts say that the disease could be controlled or even eradicated with proper inoculation rates – generally defined as 95% of a community receiving the vaccine.

But vaccination rates have dropped in some communities in recent decades as a loose network of vaccine sceptics have, without evidence, questioned the safety and efficacy of the shots.

Robert F Kennedy Jr, recently confirmed as US President Donald Trump’s health secretary, has faced strong criticism for his ties to these groups.

Most states require that children receive the MMR vaccine to attend school, but many, including Texas, also allow families to file a conscientious exemption – a non-medical reason to refuse a vaccine requirement.

In Texas, federal data shows that the state achieved a 94.3% vaccination rate among kindergarteners for the 2023-2024 school year, while New Mexico reached 95%.

But a state survey of Texas schools found that rates of exemptions were ticking upwards for MMR and other required vaccines.

In Gaines County, where 57 of the Texas cases were reported, exemptions have surged over the last decade. State data shows 17.62% of students had a conscientious exemption to at least one required vaccine during the 2023-2024 school year, up from 7.45% in the 2013-2014 year.

Neighbouring Terry County, home to 20 cases, saw exemption rates go from zero to 3.73% in the same time period.

Texas officials reported that of the 90 cases in their state, 85 were in people who are unvaccinated or whose vaccination status was unclear.

CBS reports that the area is home to a large Mennonite community, which typically have low vaccination rates due to the group’s religious beliefs.

Some officials are reluctant to intervene.

“We respect everyone’s right to vaccinate or not get vaccinated,” Albert Pilkington, CEO of the nearby Seminole Hospital District, told the Texas Standard. “That’s just what it means to be an American, right?”

US children have been vaccinated against measles since 1963. The jab was improved and combined with vaccines for the mumps and rubella viruses about a decade later, and is widely considered to be safe.

Prior to the vaccine’s introduction, around 48,000 people were hospitalized with measles each year and 400–500 people died. In 2024, the US reported 285 cases with 114 hospitalisations.

Health officials in New Mexico are offering a free vaccine clinic this week in an effort to boost protection. Texas also directed residents to contact their doctors or visit a clinic to get vaccinated if they have not previously received a shot.