US infectious disease expert Dr Anthony Fauci said that the Delta variant now makes up more than 20 per cent of all new cases in the US, nearly doubling from nearly 10 per cent two weeks ago.

“The transmissibility is unquestionably greater” in the Delta variant than the original variant of COVID-19, Fauci said, adding that “it is associated with an increased disease severity.”

The Delta variant is becoming the globally dominant version of the disease, the World Health Organization’s chief scientist said on Friday.

More than 150 million people in the United States, or more than 45 per cent of the population, have been fully vaccinated, according to federal data last updated on Monday.

Fauci said that the vaccines authorised in the United States, including the Pfizer/BioNTech vaccine, are effective against the new variant of COVID-19.

The Delta variant contributed to a severe outbreak of COVID-19 in India during April and May that overwhelmed health services in the country and killed hundreds of thousands.

The Delta variant recently became the dominant strain in the UK, surpassing the Alpha variant first discovered in the country. The strain makes up more than 90 per cent of new cases and delayed the UK’s scheduled reopening.

The transmissibility of Delta variant is unquestionably greater than the wild type SARS-CoV2 as well as the Alpha variant, Fauci said, adding that it is associated with increased disease severity as reflected by hospitalisation risk compared to the Alpha variant.