A second round of COVID-19 vaccinations for third-year high school students and school staff began on Monday.

According to the Central Disease Control Headquarters, the second round will run through August 20.

Some 96-point-eight percent of 649-thousand people, or approximately 628-thousand people, in the group received their first Pfizer shots between July 19 and 30.

Authorities asked those who experienced side effects, such as inflammation of the heart after the first shot, to postpone their second until further notice.

Those who experience chest pains, difficulty or pain when breathing or a rapid heartbeat after the second shot were urged to seek medical assistance.

Meanwhile, first round Pfizer vaccinations for some 95-thousand students outside the school system who are scheduled to take this year's College Scholastic Ability Test(CSAT) will run from Tuesday to Saturday.