South Carolina's measles outbreak — the worst in the U.S. in more than 35 years — is over, state health officials declared Monday.

On Sunday, the state passed the threshold of 42 days with no new outbreak-related cases. In the end, 997 people were sickened by the vaccine-preventable disease since October and at least 21 of them were hospitalized, based on voluntary reports to the state. State health officials estimate the outbreak response cost $2.1 million.

READ MORE: Babies too young for MMR vaccine become 'sitting ducks' in measles outbreaks

"The outbreak was predominantly contained to one area of one county and never went statewide, thanks to timely investigations, identification of those exposed, and people's willingness to stay home," said Dr. Edward Simmer, interim director of the South Carolina Department of Public Health.

Measles is one of the most contagious viruses known to medicine. Most recover after a high fever, cough, runny nose and a telltale rash. But some, including very young children and people with weak immune systems, can get pneumonia, brain swelling or even die. Measles can also cause health problems later in life for those who recover. The vaccine is safe and 97% effective after two doses.

Outbreak spurred some to get vaccinated

Centered in northwestern Spartanburg County, the measles outbreak was the fastest-growing the U.S. has seen in decades, state health officials said. Public health officials confirmed more than 650 cases in January alone, and the outbreak quickly eclipsed the 2025 outbreak in West Texas that sickened at least 762 people and killed two school-age children.

READ MORE: Dr. Mehmet Oz urges public to take the measles vaccine as U.S. cases rise

But a sooner-than-predicted decline in cases came as welcome news to doctors and health workers. A few things may have helped, Dr. Brannon Traxler, chief medical officer for the state health department, said last week. To some extent, it's possible that the outbreak waned as more people got sick, she said, but more people also got vaccinated.

While uptake was slow to begin with, public health workers, doctors' offices and pharmacies administered nearly 82,000 measles vaccines from October to March. That was an increase of more than 30% from the same time period a year prior. Spartanburg County saw a 94% increase in vaccinations.

The public health department also worked to contain the spread, sending nearly 2,300 quarantine letters, making more than 1,670 case investigation calls and working across seven school districts to quarantine 874 students.

The U.S. is on pace for more cases than last year

Measles continues to spread nationwide. So far this year, the U.S. has logged 1,792 cases — nearly 80% of 2025's record-breaking total — and 22 new outbreaks. Florida has confirmed 134 cases this year and Texas has 180, according to the Centers for Disease Control and Prevention.

WATCH: What to know about South Carolina's big measles outbreak and who is most at risk

Of greatest concern now is an outbreak that started on the Arizona-Utah border and has since spread across much of Utah. Since August, 607 people have been sickened in Utah. Mohave County, Arizona, has also confirmed 282 cases. Genetic analysis indicates the outbreak could have started six weeks earlier and may have been much larger than reported, according to research presented at a CDC conference last week.

Cases have slowed a bit, but it's still too soon to say an end is in sight, said Dr. Ellie Brownstein, a Utah pediatrician and president-elect of the state's American Academy of Pediatrics chapter. State data show that southwestern Utah still has the most cases — 258 — but each of the state's 13 local health districts has logged at least one case.

"It has marched through the state and is everywhere," Brownstein said.

South Carolina officials are still on guard

In South Carolina, the end of the outbreak has given health workers only a slight reprieve. Last week, a case linked to international travel in Saluda County, west of Columbia, led to 41 people having to quarantine.

"We are certainly not letting our guard down, and I don't think that South Carolinians who are still vulnerable to the virus, that don't have immunity, should let their guard down," Traxler said.

The virus has resurged across the Americas since a major outbreak started in Canada in fall 2024. In the U.S., childhood vaccination rates against the measles have fallen for years, as more parents opt out of shots required for school. In November, international health officials will determine if the U.S. has lost its measles elimination status, which it has maintained since 2000.

Dr. Martha Edwards, president of the South Carolina chapter of the AAP, said the end of the outbreak brought a mix of gratitude and anger.

"I'm angry that many children and their parents had to worry about contracting or suffering through a disease that should have been nearly 100% preventable," she said.