Two days before Christmas, with the Omicron variant driving a near-vertical rise in new coronavirus cases, the director of the Centers for Disease Control and Prevention alerted the White House that she planned to recommend that people infected with the virus isolate for five days instead of 10.

The director, Dr. Rochelle P. Walensky, had faced previous criticism for issuing recommendations that confused the public and in some cases caught the White House off guard. Determined to avoid that this time, she briefed other top Biden health officials on her proposal so they would all be on the same page, according to two people familiar with her actions.

It did not work out that way. Dr. Anthony S. Fauci, the nation’s top infectious disease expert, and Dr. Vivek H. Murthy, the surgeon general, were concerned that the new guidance did not urge people to get a negative Covid test before ending their isolation. After the new recommendation became public, they both took issue with it on national television, saying they expected the C.D.C. to clarify its advice.

On Wednesday, nine days after the guidance was issued and a day after it was slightly modified to include some advice on testing, the C.D.C. was still having a hard time explaining itself. “How do you expect people to keep track of what they can and can’t do?” a CNN reporter demanded of Dr. Walensky at a White House briefing.