Centers for Disease Control and Prevention officials said the guidance is in keeping with growing evidence that people with the coronavirus are most infectious in the two days before and three days after symptoms develop.
The decision also was driven by a recent surge in COVID-19 cases, propelled by the omicron variant.
Early research suggests omicron may cause milder illnesses than earlier versions of the coronavirus. But the sheer number of people becoming infected - and therefore having to isolate or quarantine - threatens to crush the ability of hospitals, airlines and other businesses to stay open, experts say.
SEE ALSO: CDC cuts isolation restrictions for those who catch COVID, recommends shorter quarantine for all
One Philadelphia emergency room doctor described the surge during the winter months as the perfect storm for the spread of the virus.
"It's spreading like wildfire. It's really impressive amounts of transmission," said Dr. Darren Mareniss who works in the ER at Einstein Medical Center.
He says vaccinated residents are among the patients coming down with omicron.
"It can happen certainly but they are protected from hospitalization and death, that's the purpose of the vaccination," said Mareniss.
According to the latest data from the CDC collected by the Action News Data Journalism Team, New Jersey is being hit the hardest, averaging over 14,000 cases a day. That's a whopping 220% increase from two weeks prior.
Delaware is seeing over a thousand new cases a day, up 67% from two weeks prior.
And Pennsylvania has 9,175 new daily cases. That's up 10% from the previous two weeks.
In the last two weeks, 15.9% of COVID-19 tests in Philadelphia have come back positive. The city is averaging 1,462 cases of COVID per day over the last two weeks.
Mareniss says if there was ever a time for people to be taking every precaution, the time is now.
"Many of our hospitals are at capacity and really cannot take any more patients," said Mareniss.
Medical professionals say if you're feeling ill, contact your doctor or go to urgent care. If you believe it could be a life-threatening issue, doctors urge you to call 911.
Officials continue to warn residents not to go to the emergency room to simply get tested for the virus.
The Associated Press contributed to this report.