North Korea continues to report zero cases of COVID-19 after testing an additional 1,436 people, according to the World Health Organization (WHO), as state media warns that “highly infectious” mutated viruses could emerge.

The latest round of polymerase chain reaction (PRC) tests conducted from Jan. 7-20 brings the total number of people screened in the country to 52,772, the WHO’s weekly situation report shows. The accuracy of the DPRK’s COVID-19 figures could not be independently confirmed.