Dr. Walensky, a highly regarded infectious disease expert from Boston with no prior government experience, insisted in February that schools must keep students six feet apart; in March, she said three feet was enough. She said in February that teachers did not need to be vaccinated to reopen schools; the White House said the next day that she was speaking “in her personal capacity.”

In May, she said that vaccinated people generally did not need to wear masks in public, a sudden change that flummoxed state health officials. Two months later, she reversed that guidance after it was shown that vaccinated people could still transmit the virus.

With the virus throwing one curveball after another, changing advice from the C.D.C. is a given. But Dr. Walensky’s critics say the C.D.C.’s recommendations are sometimes so confusing or abruptly modified that they seem more like drafts than fully vetted proclamations…

“The new recommendations on quarantine and isolation are not only confusing, but are risking further spread of the virus,” the American Medical Association said in a statement on Wednesday.