Dr. William Moss likens the Maryland’s first case of measles this year to the spark that causes a forest fire.

If it lands in a place that isn’t susceptible to burning, nothing happens. But if the place is a ripe target, the spark triggers a blaze.

“There are high vaccination rates in Maryland, so there are fewer” at risk, said Moss, an infectious disease expert at Johns Hopkins University. “But there are still pockets.”

Those pockets in Maryland and around the country have long concerned Moss and other public health officials. Measles is highly contagious and potentially dangerous to a patient’s health in the short and long term. It’s also costly for health officials to treat and public health officials to trace to other people.

The Maryland Department of Health released few details of the case that was disclosed Sunday, but warned the public about the person’s travels through Baltimore-Washington International Thurgood Marshall Airport on April 12; FastMed Urgent Care in Pikesville on April 14; and the pediatric emergency department at Sinai Hospital in Northwest Baltimore on April 17.

Moss said that’s a lot of places to pass an infection to the unvaccinated, including health care facilities potentially with unvaccinated infants, pregnant people and immunocompromised patients.

Those with measles remain contagious for more than a week: four days before the telltale red rash appears until four days afterward.

It’s so transmittable that a person can be infected walking through droplets left hanging in the air two hours after someone with measles coughed, said Moss, who is also executive director of the Johns Hopkins University’s International Vaccine Access Center.

In Maryland, high vaccination rates are good news. That’s because the combination measles-mumps-rubella vaccine is needed to enter kindergarten, with few exceptions.

Data provided by the health department showed that during the last school year, more than 96% of students had their required two doses. That level helps establish so-called herd immunity, offering protection to the larger community.

Garrett and Allegany counties in Western Maryland and Baltimore City fell just below the mark. The lowest rate was in Kent County, where a high rate of religious exemptions kept the rate to 86.5%.

Maryland reported just five measles cases in the last five years. But around the country in 2025, there were 2,288 cases, mostly in Texas, Utah, Florida and South Carolina.

And Moss and others fear that more people might go unprotected with the rise in vaccine skepticism spurred on by U.S. Secretary of Heath and Human Services Robert F. Kennedy Jr. He and his supporters have challenged the vaccine’s safety, without evidence, for most people.

Health officials encourage parents to vaccinate their kids and check their own status.

Among adults, anyone born after 1989 — when the two-dose regimen was introduced has strong protection if they got the shots. Those born before vaccination began in 1957 are considered protected because they were likely infected and have lifelong immunity.

From 1967 to 1989, those who got one dose still likely have protection of at least 90%, and Moss said they could get a second dose if they are concerned.

Between 1963 and 1967, people sometimes received an ineffective vaccine, so they should talk to their doctors about getting another shot, he said.

The health department said insurance generally covers the vaccine, and state and federal programs cover those uninsured or underinsured through their local health departments.

“Vaccination remains essential to protecting ourselves, our families, and our communities against measles and other infectious diseases,” Dr. Meg Sullivan, Maryland’s deputy secretary for public health services, said in a statement.

Measles can mean being out of commission for a long time.

First there is a week with a head-to-toe rash, fever, runny nose and cough, symptoms that usually develop from one to three weeks after exposure.

And those exposed and unvaccinated also need to quarantine for three weeks, missing school and work. Identifying them and who they may have been in contact with also is a huge public health burden, said Dr. Georges Benjamin, executive director of the American Public Health Association.

A Johns Hopkins analysis found that the average cost of tracing a case was $43,000, including monitoring, testing and communicating the threat.

Benjamin, also a former Maryland health secretary, said that the state has done a good job on vaccinations and most who get measles recover. But a big rash and a big bill aren’t the only considerations.

The illness comes with potentially dangerous secondary infections, such as pneumonia or brain swelling, known as encephalitis. Measles killed three people, including two children last year, in the United States.

Measles can leave a person’s immune system unable to fight off other infections, a condition that usually lasts weeks or months but sometimes can continue for years.

Rarely, measles also leads to much more serious problems, including a fatal neurological condition, miscarriage or stillbirth.

“At the end of the day measles is preventable,” said Benjamin. “There is enormous benefit to protecting yourself as an individual but also for society.”