The CDC doesn't require testing at end of isolation. Here's why

The newly updated CDC guidelines don't require testing at the end of isolation because PCR tests can stay positive for up to 12 weeks, CDC Director Dr. Rochelle Walensky told "Good Morning America" on Wednesday.

"So we would have people in isolation for a very long time if we were relying on PCRs," Walensky said.

Walensky also addressed Tuesday's news from the FDA that, according to early data, rapid antigen tests may be less sensitive when it comes to the omicron variant.

"We do know that the most sensitive test you can do is a PCR test," Walensky said. "So if you have symptoms and you have a negative antigen test, we do ask you to go and get a PCR to make sure those symptoms are not attributable to COVID."

Walensky said rapid tests do work "quite well," especially in places where people are being tested regularly, like at schools.

The World Health Organization says the number of COVID-19 cases recorded worldwide increased by 11% last week compared with the previous week, with the biggest increase in the Americas.

"They may not work as well as they have for the delta variant," Walensky said, but "we still are encouraging their use."

CDC COVID-19 Transmission Levels by U.S. County

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