WASHINGTON (NYTIMES) - The Centres for Disease Control and Prevention (CDC) on Monday (Dec 27) shortened by half the isolation period for people who contract the coronavirus, saying that just five days after their positive test results those without symptoms could safely resume mixing with others.  

That replaced previous guidance from the agency that infected patients isolate for 10 days.

The agency cited growing evidence that the virus is most contagious in the two days before and three days after symptoms develop. People with symptoms after five days are encouraged to remain at home.  

The new guidance was announced as the highly transmissible Omicron variant is sending daily caseloads soaring, forcing airlines to cancel thousands of flights and cities to scuttle or scale back New Year’s Eve celebrations and threatening industries as diverse as health care, restaurants and retail.  

“The Omicron variant is spreading quickly and has the potential to impact all facets of our society,” said Dr Rochelle Walensky, director of the CDC.

The new recommendations “balance what we know about the spread of the virus and the protection provided by vaccination and booster doses. These updates ensure people can safely continue their daily lives.”

Health officials also said that uninfected Americans who had received booster shots did not need to quarantine after exposure to the virus.

The CDC has been criticised for shifting guidance and mixed messaging.

Last week, the agency recommended that healthcare workers who are asymptomatic return to work after just seven days and a negative test, adding that “isolation time can be cut further if there are staffing shortages.”

States, cities and employers can choose whether to follow the CDC’s guidance.

In New York state, which has reported record levels of cases and surging hospitalisations, major hospitals recently changed isolation protocols for vaccinated employees.  

Some places are reporting their worst caseloads of pandemic. Delaware, Hawaii, Massachusetts, New Jersey, New York and Puerto Rico have reported more coronavirus cases in the past week than in any other seven-day period, data show.  

The numbers point to the ease with which Omicron is spreading across the United States, even as some studies from overseas suggest that the variant might cause less severe illness.

Experts warn that the surge of infections, combined with the fact that tens of millions of Americans remain unvaccinated, could still create a severe strain on the US health system and lead to many more deaths.