With the spread of mumps often linked to schools and other places where people congregate, state health officials are hoping the fast-approaching end of the school year will put a dent in the current outbreak, which has reached a 16-year high with no signs of slowing down.

But it’s probably too much to expect a significant impact, said Dr. Sarah Park, state epidemiologist.

That’s because nearly half of the cases are adults, and only a few of those have confirmed links to schools, she said.

On Thursday the state Department of Health reported five more cases of mumps, bringing this year’s total to 47 in Hawaii — 46 of them on Oahu and the other on Kauai.

The department expects to see more cases because the viral disease is even more contagious than the flu.

Hawaii’s outbreak mirrors what’s going on across the United States as 42 states and the District of Columbia reported more than 2,570 cases of mumps this year through April, according to the Centers for Disease Control and Prevention. Nearly 6,000 cases were reported last year in the U.S.

Recent outbreaks in the hardest-hit states started in the latter part of 2016 and continue today, including in Arkansas, where nearly 3,000 cases have been recorded, and Washington, which has seen at least 842 cases.

In Washington, health officials report that the state’s outbreak has largely been linked to schools and people in contact with schools and students.

In 2009 and 2010 about 500 mostly school-age children were stricken on Guam.

Children are certainly known to be more susceptible to the disease, and schools are places where kids come together and inadvertently pass the infection to others.

And while about 90 percent of Hawaii’s students are vaccinated for mumps, two doses of the vaccine are only 88 percent effective, which leaves 12 out every 100 students vulnerable, officials say.

In Hawaii, officials report that cases of mumps have been linked to Central Middle School and at least nine other schools.

With Hawaii’s public school system ending its instructional year a week from today, the elimination of these gathering places could provide some relief.

“This might be very fortunate,” said Dr. Marian Melish, professor of pediatrics at the University of Hawaii’s John A. Burns School of Medicine. “School is a good place to spread it around.”

But how much help is hard to say, Melish said, adding that schoolchildren are among the most vaccinated in the general population.

Park said that while she hopes the end of the school year will help knock down Hawaii’s outbreak, she’s not sure it will do much. The problem, she said, is that 21 of the 47 cases are adults, many of whom don’t have any obvious connection to schools.

What’s more, she said, there are only a few cases at each campus, which indicates that links to schools are probably not the issue.

“I’m not sure it will solve the problem,” Park said of school’s end. “It might help, it might not. It’s hard to say.”

Melish said Hawaii’s outbreak is part of the larger epidemic across the U.S., with the disease likely arriving here with somebody who picked up the infection on the mainland.

On the mainland the disease has taken off at numerous college campuses in recent years. There’s growing evidence that immunity diminishes beyond five years after receiving the mumps vaccination, prompting the CDC to consider adding a third dose in the series of mumps shots, Melish said.

Even if the vaccine isn’t perfect, it has prevented scores of infections over the year, she said. About 186,000 cases were reported each year prior to the start of the U.S. mumps vaccination program in 1967.

Melish said an epidemic can be especially difficult to control because about a third of those who get the mumps have no symptoms.

“They could be major spreaders,” she said.

Melish, who is in charge of infection control at Kapiolani Medical Center for Women &Children, said she would not be surprised if Hawaii’s outbreak reaches 100 or 200 cases.

“Even if there were 200 cases in a population of 1 million, that’s not too amazing,” she said.

Both Melish and Park said there’s no need to panic.

“It’s not such a terrible thing,” Melish said. “It’s a highly contagious disease, but the symptoms are not very severe.”

So far, no one in Hawaii this year has needed to be admitted to a hospital due to the mumps, officials said.

Symptoms include a swollen jaw, fever, headache, muscle aches, tiredness and loss of appetite.

The disease is spread through coughing and sneezing, close contact or touching something that is contaminated, then touching the eyes, nose or mouth.

Officials say patients suspected or diagnosed with mumps should stay home and avoid going out and exposing others for nine days after the onset of swelling of the salivary glands in the jaws.

Anyone who has been exposed to mumps and is not vaccinated should not attend school, work or travel from 12 through 25 days after exposure, they said.