(Reuters) – Teachers may play an important role in the transmission of COVID-19 within schools, the U.S. Centers for Disease Control and Prevention (CDC) said on Monday, citing a study conducted in elementary schools in a Georgia school district.

The report comes after researchers from the agency last month said there was little evidence that schools were spreading COVID-19 infections in the country – based in part on a study of schools in Wisconsin – easing concerns about allowing in-person learning. The Wisconsin study found significantly lower virus spread within schools compared with transmission in the surrounding communities.

An investigation involving about 2,600 students and 700 staff members of a Georgia school district’s elementary schools showed nine clusters of COVID-19 cases involving 13 educators and 32 students at six elementary schools, the CDC said.

Of these, two clusters involved probable teacher-to-teacher transmission that was followed by teacher-to-student transmission in classrooms, the agency said in its Morbidity and Mortality Weekly Report.

Transmission from teachers resulted in about half of 31 school-related cases, according to the investigation.

The study was subject to some limitations including difficulty in determining whether coronavirus transmission happened in school or out in the local community, the agency noted.

Distinguishing between the two types of transmission was particularly challenging when the 7-day average number of cases per 100,000 persons exceeded 150, the agency said.

The CDC said COVID-19 vaccination of educators should be considered as an additional mitigation measure to be added when available, although not required for reopening schools.

(Reporting by Manojna Maddipatla in Bengaluru; Editing by Bill Berkrot)