The government is mulling whether to open a fourth round of COVID-19 shots to all citizens in the second half of the year as it studies possible infection trends at home and abroad.

A senior official at the Central Disease Control Headquarters, Lim Sook-young, said on Tuesday that although 19 in 20 South Koreans have developed antibodies against COVID-19, any imparted immunity could wane by this fall, making vaccination plans crucial to the prevention of another spread.

She said if immunity diminishes quickly, it could trigger another wave sooner than expected, but the resurgence could be delayed by vaccinations.

Authorities are drawing up countermeasures against another possible wave of COVID-19 in the second half of the year, focusing on vaccinations, treatment regimens and monitoring new variants.

Seniors aged 60 and older began receiving their fourth shot in April of this year, with over 34 percent of the more than 12 million people in the age group having received the shot to date.