The number of breakthrough COVID-19 infections in South Korea is rising rapidly. 

The Central Disaster and Safety Countermeasures Headquarters said on Wednesday that an estimated total of 647 people tested positive for the virus as of 12 a.m. even after they were fully vaccinated. 

The tally has more than doubled from 252 recorded on July 8. While the number for July 8 has been confirmed, Wednesday’s tally are preliminary figures. 

Recipients of the Johnson & Johnson vaccine made up for a majority of breakthrough cases at 364, followed by the AstraZeneca vaccine at 148 and the Pfizer vaccine at 145.  

Health authorities stressed breakthrough patients have a low risk of degenerating into serious conditions with just four out of the 647 cases so far categorized as serious. None have so far been fatal.