MISSION, Ore. (AP) — The Confederated Tribes of the Umatilla Indian Reservation has seen a rise in COVID-19 cases among school children, prompting officials to schedule more vaccination clinics and cancel events.

The Tribes reported on Wednesday that 14 people had tested positive for COVID-19 on the reservation over the past two weeks, The East Oregonian reported.

Tribal officials said the outbreak came after six weeks without one case reported among tribal members and patients eligible for care at Yellowhawk Tribal Health Center. The 12 children who have the illness reportedly experienced symptoms and one adult was hospitalized in the outbreak, officials said.

“The virus is spreading among our youth and we need to respond immediately,” Lisa Guzman, Yellowhawk Tribal Health Center chief executive officer, said while announcing a Saturday vaccination clinic for those age 12 to 15.

Wildhorse Resort & Casino announced Thursday that the annual Wildhorse Pow Wow set for early July would be canceled for the second year because of rising cases and risk of local spread with people coming from around the country.

The new cases brought total active COVID-19 cases on the reservation to 17, making it one of the sharpest upticks reported on the reservation since 19 cases were reported in a week in December, according to data on the Tribes’ website.

Yellowhawk officials attempting to trace the outbreak have been met with reluctance from residents, officials said.

Since the pandemic began, tribal health officials have reported 271 COVID-19 cases, 13 hospitalizations and one death, officials said.