USA / We can't let Delta COVID-19 variant take over in US: Anthony Fauci

Washington: The highly infectious Delta coronavirus variant could become the dominant strain in the US if people don't get fully vaccinated, the US's top infectious-disease expert has warned.

Dr. Anthony Fauci, President Joe Biden's chief medical advisor, said Tuesday that the Delta variant had rapidly emerged as the dominant variant in the UK, replacing the Alpha variant.

"We cannot let that happen in the United States," Fauci said during a White House press briefing.

The Delta variant is thought to have caused record-breaking infection numbers in India, where it was first identified. A surge in coronavirus infections brought India's health system near collapse in the spring.

The Delta variant accounts for more than 6% of sequenced tests in the US and 60% of infections in the UK, Fauci said. The actual figures could be different, as not every test is sequenced. The highest rates of transmission in the UK are people ages 12 to 22, he said - a mostly unvaccinated age group.

Fauci urged Americans to get vaccinated to stop the Delta variant from spreading further in the US.

"Particularly if you had that first dose, make sure you get that second dose. If not, please get vaccinated," Fauci said in a briefing. The Alpha variant, first identified in the UK, is currently the most common virus strain in the US.

The Delta variant is at least as infectious as the Alpha variant and has now spread to more than 60 countries. It also has extra mutations that may allow it to escape the antibody response - a part of the immune system that fights the virus - so vaccines appear to offer less protection against it when just one dose is given.

A UK-based study posted on May 24 found that the Pfizer-BioNTech COVID-19 vaccine was 88% effective at preventing symptomatic COVID-19 caused by the Delta variant after two doses but only 33% effective after a single dose.

Another lab-based study from the UK posted Thursday found that the antibody response was "significantly lower" against the Delta variant compared with the Alpha variant after one dose.

The Biden administration is trying to give more than 75% of the US population at least one dose of a COVID-19 vaccine by July 4 to try to stop another surge in infections. So far, more than 51% of Americans have had at least one dose, and more than 42% are fully vaccinated, according to the Centers for Disease Control and Prevention.