SEOUL—South Korea has detected its first two cases of the new Delta Plus COVID-19 variant, the Korea Disease Control and Prevention Agency (KDCA) said on Tuesday, as the country battles with its fourth wave of infections. The Delta Plus variant is a sub-lineage of the Delta variant first identified in India, and has acquired the spike protein mutation called K417N, which is also found in the Beta variant first identified in South Africa. Reports of Delta Plus cases have been few, and a handful of countries, including Britain, Portugal and India, have reported some cases. “The first case (in South Korea) was identified in a man in 40s who has no recent travel records,” the KDCA told Reuters. The source of transmission is under investigation. Test results in around 280 people who were in contact with the man found that only his son was positive too, Park Young-joon, a KDCA …