One-third of the 1,350 students at Maui's Kalama Intermediate School in Makawao had to stay home because of possible exposure to measles earlier this month.
About 80 were still out yesterday but some were expected to return to school today and the rest Oct. 7.
The disease is characterized by high fever, cough, runny nose and a distinctive skin rash. Complications include pneumonia, ear infection, encephalitis and, occasionally, death.
Two doses of MMR vaccine (combined for measles, mumps and rubella) are required for school entry, said Dr. Paul Effler, chief of the Epidemiology Branch.
That rule wasn't enacted until 1994, however, and kids already in school at that time may have gotten only one shot, he said.
About 95 percent of people are protected with one shot, but it may not work in up to 5 percent of people so they're "likely to be involved in an outbreak," he said.
"There have been sustained measles outbreaks in other parts of the country where kids had a first MMR because measles is so infectious," he said. "It is probably the most infectious disease known to man."
Effler said the Public Health Nursing Branch has been asked to try to identify children with only one vaccination and recommend a second shot.
At Kalama School, he said, about three-fourths of the students had two doses of vaccine but 25 percent had only one.
The Health Department gave 170 vaccinations to students in three days after two children, ages 9 and 13, and their mother were infected with measles.
None had been immunized for religious reasons, Effler said.
The 9-year-old was diagnosed with measles Aug. 29. When school began Sept. 3, the 13-year-old sibling received a first MMR vaccination, but became ill three days later with measles. The children's mother was reported infected Sept. 8.
The Health Department cautioned that all students and staff at the school from Sept. 3-6 were potentially at risk for measles.
"Everybody in school now has met all immunization requirements," said Kalama Principal Stephen Yamada.
Initially, 452 students were kept out of school. Some were allowed to return immediately if they had been vaccinated once and received a second shot, he said.
Religious exemptions had been granted to 26 Kalama students. Of those, 12 got immunized, but 14 are out of school until Oct. 7, according to the Health Department.
Those with no immunizations who got the first shot had to stay home 14 days, Yamada said. Those who couldn't be immunized for medical or religious reasons had to stay out 28 days.
The Maui cases were the first confirmed cases of measles here since 1994, the Health Department said.
Effler said the first dose of MMR vaccine should be given at 12 to 15 months of age; the second between 4 to 6 years. The virus can be transmitted to others even before symptoms occur, he said.