GUILDERLAND — Between Dec. 29 and Jan 4, during Christmas vacation, the Guilderland schools had 21 new cases of COVID-19, according to an email Superintendent Marie Wiles sent to GCSD Families on Monday evening.

Only two of the cases required contact tracing, she wrote, and those people are already under quarantine. Wiles noted that, as of Dec. 16, the state’s health department adopted the Centers for Disease Control and Prevention guidelines and decreased the quarantine period from 14 days to 10 days.

Cases were reported at these schools:

— Ten at Guilderland High School;

— Six at Farnsworth Middle School;

— Two at Westmere Elementary School;

— Two at Altamont Elementary School; and

— One at Pine Bush Elementary School.