Minnesota has reported its first case of measles this year, in someone who may have spread the highly infectious disease to others while traveling in Washington, D.C.

DC Health issued an alert Tuesday saying the individual had visited multiple locations and may have exposed others on March 19 while riding an Amtrak train or walking through a concourse at Union Station in Washington. The individual sought treatment on Saturday at a D.C. urgent care location, making it a third possible exposure site.

"The individual was not infectious while in Minnesota," said Jayne Griffith, an infectious disease epidemiologist for the Minnesota Department of Health. "We are still investigating where this individual may have acquired measles."

The case comes amid declines in Minnesota's measles vaccination rate, and an outbreak of 77 cases last year that was the state's second-highest in at least 35 years. However, the current case involved someone who had been vaccinated, receiving two doses of MMR vaccine.

"It is 97 percent effective at preventing measles," Griffith said of the vaccine. "Still, that means up to 3 in 100 people who get vaccinated for measles may still get sick. ... This appears to be one of those very rare cases."

Griffith noted that even rare cases of measles among vaccinated individuals tend to involve milder symptoms than unvaccinated cases.

D.C.'s chief epidemiologist, Brittani Saafir-Callaway, told the Washington Post that the person was not contagious when flying into Reagan National Airport. Close contacts of the individual on the train were being notified and monitored for symptoms.

"D.C. has a very high vaccination rate for measles, so the opportunity for an outbreak in the district is very low," Saafir-Callaway said.

The unidentified individual had been traveling on Amtrak's Northeast Regional 175 train, which runs between Boston and D.C.

The measles virus is one of the most infectious agents on the planet, capable of lingering in the air and spreading to others long after sick people have left. Known by its characteristic head-to-toe rash, measles also causes high fevers, cold symptoms and breathing problems.

Hesitancy over the COVID-19 vaccine during the pandemic has resulted in more parents declining other vaccines for their children, including the measles vaccine traditionally given in two shots before children enter grade school.

Minnesota once ranked among the best states with about 94% of its children vaccinated against measles by the time they entered kindergarten. That rate dropped to 87% at the start of the 2022-2023 school year, which was sixth-worst, a recent federal report showed.

Unvaccinated people have been at the epicenter of outbreaks this winter in Texas, New Mexico and Oklahoma. The Centers for Disease Control and Prevention has confirmed 378 infections through March 20, including one death of a child. A second death remains under investigation. About 1 in 5 of infected individuals was admitted to hospitals for treatment. Most of the cases involve children and teenagers, but about 1 in 4 involves people 20 and older.

Minnesota's 2024 outbreak had vexed public health officials at one point last summer when they identified infections in children who lived in three metro-area counties and had no apparent connections. They later determined the cases all likely linked back to children who had been exposed to measles during travels to other countries where the infectious disease is widespread.

The outbreak was largely among unvaccinated children in Minnesota's Somali community, which has been particularly hesitant over pediatric vaccinations.