The absentee rate at Hamilton-Wenham Regional High School rose to 9.4 percent earlier this month - more than double the usual rate.
The increase was largely attributed to the elevated cases of influenza this year, said the Hamilton Board of Health.
So far, 12 cases of flu have been formally reported in Hamilton, according to the Board of Health. The age of those with the flu have ranged from 4 months old to 82, with five cases in children under age 8 and one over age 65.
Townwide, cases have been up, according to health officials. The last two flu season were very light.
In early January, the absentee rate at the high school was 8.7 percent for the first week back from the holiday vacation and then rose to 9.4 percent for the week of Jan. 6-11, according to the Board of Health.
The typical absentee rate is about 3.5 percent, according to data provided by the Hamilton-Wenham Regional School District.
This fall, the Board of Health distributed 425 doses of vaccine at two separate flu vaccine clinics. The town is out of vaccine but it has still be available nearby, including recent clinics at Beverly Hospital and Addison Gilbert Hospital in Gloucester. Doses have also been available at Family Medicine Associates in Hamilton and at most pharmacies, including CVS.
The Board of Health said that the absentee rate of school staff has not been high.