Fifteen school students in Hangzhou, Zhejiang province have tested positive for COVID-19, said the city's health authorities on Monday.

The cases — 10 at a primary school in Xihu district and five at a secondary school in Gongshu district — were all infected for the first time, according to authorities.

The two schools announced that in-person attendance for infected students and those in close contact with them has been temporarily put on hold as per COVID-19 prevention and control plans formulated after China optimized its COVID-19 response measures in December last year.

"Their symptoms are quite mild, with some coughing and several have already recovered," revealed Zhang Junlin, principal of the primary school.

Over half of the students in the school haven't caught COVID-19 at all so far, and the vast majority of unaffected students went to school as usual on Monday, he said.

Recovered students are expected to return to school once the required class suspension from Monday to Thursday is over.

Despite the relaxation of COVID-19 restrictions two months ago, health authorities in Hangzhou and across China are still closely monitoring its development and the emergence of new cases.

"In general, schools are advised to suspend in-person attendance for a class once more than 20 to 30 percent of students in that class are infected with COVID-19," a staff member from the Xihu district center for disease control and prevention explained.

A set of guidelines issued by Zhejiang Provincial Department of Education in 2018 stipulated that the class size of a primary school should not exceed 45 students while that of a middle school should be kept below 50.

These infected students are isolated cases, said an official with Hangzhou's COVID-19 prevention and control command center, and it does not signify the start of a new wave of infections.

Meanwhile, 12 students at a primary school in the city's Shangcheng district reported symptoms of fever and were found to be a cluster infection of influenza. In-person attendance and teaching schedules for these students and their classes have been rearranged as per health protocols.

Parents are advised to take their children to get antigen tests should they have any fever and similar symptoms, said the command center.

But as it is currently also a period of high incidence for H1N1 and norovirus infections, children who develop these symptoms do not necessarily have COVID-19, it added.

The center has urged residents to continue observing good hygiene, including washing hands frequently, wearing masks properly and maintaining proper ventilation.

"There is nothing to worry or panic about," a parent whose kid attends the COVID-affected primary school told local media, as long as necessary protection measures are taken.

mazhenhuan@chinadaily.com.cn