Washington — Dr. Anthony Fauci, chief medical adviser to President Biden, said Sunday that the administration is weighing the addition of a negative COVID-19 testing requirement to its guidelines for isolation —amid a backlash against the Centers for Disease Control and Prevention (CDC) after it halved the isolation period for those who are asymptomatic. Fauci told ABC News' "This Week" that Americans would likely be hearing more about changes to the CDC's isolation guidelines for people who test positive for COVID-19 "in the next day or so" after there was "some concern" about why current instructions do not include a testing requirement for asymptomatic people at the end of the five-day isolation period. "That is something that is now under consideration," Fauci said. "The CDC is very well aware that there has been some pushback about that. Looking at it again, there may be an option in that, that testing could be a part of that." The CDC announced last week that Americans who test positive for COVID-19 and are asymptomatic need to be isolated for five days, cutting the isolation period from 10 days. Under the new guidelines, those with COVID-19 who do not show symptoms must also wear masks for a five-day period after their isolation ends. The agency also eased guidance for quarantining after exposure to COVID-19. Those who are fully vaccinated and have received a booster do not need to quarantine after exposure, while unvaccinated Americans or those who are eligible for a booster but have not yet received the added shot must quarantine for five days, followed by mask-wearing for five more days. If a five-day quarantine is "not feasible," an unvaccinated or not-yet-boosted person who is exposed to COVID-19 must wear a mask around others for 10 days, the CDC said. The change in the isolation guidelines was motivated by data showing the majority of transmission occurs early in the course of illness, typically within two days before the onset of symptoms and up to three days after, according to the CDC. The eased measures come as the fast-spreading Omicron variant drives a surge of new infections, leading to record numbers of cases and hospitalizations in some places and fueling a shortage of COVID-19 tests in the United States. Some speculated the lack of a testing requirement in the CDC's update guidelines was due to the short supply of COVID-19 tests, but Dr. Rochelle Walensky, the agency's director, told "CBS Mornings" last week that wasn't the case. "It had everything to do with knowing what we would do with the information when we got it," she said. Walensky said requiring PCR tests to end isolation "would not be viable" because they can detect remnants of COVID-19 for up to 12 weeks, even after a person is no longer contagious.