US health authorities on Monday shortened the recommended isolation time for Americans with asymptomatic cases of COVID-19 to five days from the previous guidance of 10 days.

The Centers for Disease Control and Prevention also said the asymptomatic people after isolation should follow five days of wearing a mask when around others.

It also recommended a five-day quarantine for those exposed to the virus who are unvaccinated or are over six months out from their second mRNA dose or more than two months after the Johnson & Johnson vaccine and not yet boosted. The quarantine period should be followed by strict mask use for an additional five days.

According to the CDC, isolation separates sick people with a contagious disease from people who are not sick, while quarantine separates and restricts the movement of people who were exposed to a contagious disease to see if they become sick.

"CDC's updated recommendations for isolation and quarantine balance what we know about the spread of the virus and the protection provided by vaccination and booster doses," CDC Director Rochelle Walensky said in a statement.

Omicron accounts for 73% of U.S. coronavirus infections, the federal CDC had said last week.

Breakthrough infections are rising among the fully vaccinated population, including those who have had a third booster shot. However, Omicron appears to be causing milder symptoms in those people, some of whom have no symptoms at all.

Reducing the CDC's 10-day quarantine recommendation would help asymptomatic people return to work or school, with proper precautions, White House medical adviser Anthony Fauci had told CNN last week.

Individuals who have received their booster shot do not need to quarantine following an exposure, but should wear a mask for 10 days, the CDC said.