Health authorities have raised the alarm on a possible explosive resurgence of COVID-19, noting that infections are spreading nationwide.

In a Friday briefing, Kwon Jun-wook of the Korea Disease Control and Prevention Agency(KDCA) said the virus reproduction rate has passed one-point-22 across the country. This level of outbreak can only be suppressed by having at least 20 percent of a community fully vaccinated, he said. 

The reproduction rate refers to the number of transmissions caused by a single patient. A figure above one means the disease is spreading.

Kwon said that if last year is any guide, surges led to smaller scale outbreaks and it took a substantial amount of time to curb the spread. He stressed the importance of managing what he called "core groups" that consist of unvaccinated people who can spur a spike in cases. 

The official said basic safety rules must be observed at rallies and protests, religious gatherings and entertainment venues that draw younger crowds.