Beijing: China, the nation which was seen struggling to contain a surge at the start of the year, has also registered the highly contagious XBB new sub-variants of the COVID-19 infection, media reports said.

There were 12 new sub-variants detected in the past week in China, reports Shine.

From December 1 to April 20, the nation reported 32,993 effective genomic sequences of domestic cases. All were confirmed as Omicron variants covering 117 sub-variants, with BA.5.2 and BF.7 as dominants, according to the weekly report issued by Chinese Center for Disease Control and Prevention on Saturday, the news portal reported.

The centre detected 603 cases of variants under strict inspection, including the 12 sub-variants being found for the first time.

A total of 42 cases with XBB.1.16 were reported in the previous and this weekly report.

The 15 cases of Omicron sub-variant XBB.1.16 were reported for the first time in the last report on April 15. The other cases were in this week's report.

According to Zhang Wenhong from Huashan Hospital, director of the National Center for Infectious Disease, the coronavirus may cause a second infection six months on due to variations but prevalence is usually not large, reports Shine.

But if the next round of variation surpasses the immunity barrier established by the first round of infection, the second infection also can cause a peak.