Washington,  Even as Omicron has now become the dominant variant in the US, the country has reported its first death from the highly transmissible variant, the media reported.

An unvaccinated man in his 50s with underlying health conditions is believed to have been the first American to die from the Omicron variant of Covid, Fox News reported.

Harris County Judge Lina Hidalgo confirmed on Monday in a tweet that he became the first to die from Omicron in the county.

"Sad to report the first local fatality from the Omicron variant of Covid-19. A man in his 50's from the eastern portion of Harris County who was not vaccinated," Hidalgo tweeted.

"Please - get vaccinated and boosted," she added.

The death comes as Omicron is spreading rapidly throughout the US, replacing Delta as the dominant strain and accounting for over 73 per cent of new weekly cases, according to the Centers for Disease Control and Prevention's (CDC) latest estimates.

The Omicron variant is spreading rapidly nationwide and has been found in at least 48 states till date, since the first case in the country was detected in California on December 1.

The infection cases caused by the Omicron variant jumped from 12.6 per cent of all infection cases in the week ending December 11 to 73.2 per cent in the week ending December 18, the CDC estimates published on Monday showed.

The US continues to be the worst-hit country with the world's highest number of cases and deaths at 51,097,528 and 807,945, according to Johns Hopkins University.

The unprecedented infectiousness of the Omicron variant and its possible ability to evade the immune system have stoked concerns. However, experts said preliminary data suggest the new variant appears to cause less severe symptoms and hospitalisations.