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 official told a briefing.

Park said it was unclear whether the son was also infected with Delta Plus.

The second case was found in a traveller who returned from the United States. The person had been vaccinated with both shots of AstraZeneca before the trip, Park said.

Health authorities have said several major vaccines work against the highly contagious Delta variant, which has already become dominant in many countries, but have raised concern new strains may evade some vaccines.

Genetic analysis of 3,014 infections last week found 64% were the Delta variant, KDCA data showed, a clear sign the variant has become the dominant strain in South Korea as well. Cases among the fully vaccinated remained low.

Some scientists have said the Delta Plus variant may be even more transmissible. Studies are ongoing in India and globally to test the effectiveness of vaccines against this mutation.

South Korea reported 1,202 new COVID-19 cases for Monday, raising the total to 202,203 infections, with 2,104 deaths.

The country on Tuesday said it has given 20 million people, or 39% of its population, at least one dose of a vaccine, while 14.1% have been fully vaccinated.

South Korea aims to immunise at least 36 million people by September.