Within CDC, there's debate about how to best advise Americans on masks

In his self-described "viral rant," the comedian ripped apart the new guidance as "too complicated" and "unreadable."

"I know science is difficult and this is a novel virus and all of that, but who's running messaging at the CDC?" Noah asked.

As CDC staff passed around a link to the April 27 monologue, a federal official told CNN, the message was clear: Noah was kind of right.

"Some people were like, 'he has a point,' " the official said.

Federal officials tell CNN there is debate within the CDC over whether the agency, in this post-vaccination world, needs to tweak its mask guidance -- making it more clear and also less strict, giving more incentive for people to get a Covid-19 shot.

"The CDC tends to be conservative in its approach, and that sometimes results, I think, in people seeing CDC guidance as just not being practical," another federal official said.

Spokespersons for the CDC did not respond to CNN requests for comment for this story. In an interview Wednesday with CNN's Chris Cuomo, CDC Director Dr. Rochelle Walensky said the agency will update its mask guidance for vaccinated people "very soon" while it awaits more data.

Incentive to get vaccinated is clearly needed: About 40% of Americans haven't gotten a Covid-19 shot yet, even though supply is plentiful.

"It's difficult, because science is very nuanced, and that's where the battle comes in," one of the federal officials said. "But if you're not willing to make science understandable and practical -- well, then you get the mask guidance."

The CDC mask guidance is coming under fire for two main reasons.

The first criticism is that the scientific data indicates the agency can be more lenient and allow for vaccinated people to take off their masks in a wider range of situations than recommended under CDC guidelines.

The second criticism is that the CDC's guidelines have been unnecessarily complicated. A CDC graphic shows 28 faces, some masked and some unmasked, against red, yellow and green backdrops denoting different levels of risk.

One of the officials remembers first laying eyes on the graphic in April and feeling that it was too restrictive and also somewhat incomprehensible.

"When I had heard the guidance was coming out, I was hoping for some big-time bone being offered to get people on board with getting vaccinated, but the guidance fell way short of that, in my opinion," the official said. "When I saw it, oh my gosh, I just said to myself, 'no, no!'"

Or as Noah put it: "The sh*t you're saying to people is incoherent."

A former CDC communications specialist said the public needs to understand clearly what steps they should be taking.

"People need to be told on a more regular basis: What are the end objectives that we're striving for?" said Glen Nowak, director of Center for Health and Risk Communication at the Grady College of Journalism and Mass Communication at the University of Georgia, who worked at the CDC for 14 years.

At a congressional hearing this week, several senators had harsh words for the agency.

"I'm incredibly frustrated, and the American people are frustrated because they hear you're following the science but then they just have a sense that the lag time between implementation of that and recommendations is just far too long," said Sen. Bill Cassidy, R-LA, a gastroenterologist who created a partnership in his state to vaccinate children against hepatitis.

Walensky said the agency is continuing to review the data.

"We are changing our guidance as the science evolves and as the science emerges, and we have to remain humbled to that science," Walensky said during the Senate hearing Tuesday.

On CNN on Wednesday, Walensky said the CDC is waiting for more data on two important questions before revising the indoor mask guidance for people who've been vaccinated.

The first concerns virus variants. Some data have shown that the Covid-19 vaccines are somewhat less effective at fighting certain variants.

"With those variants here, we do want to make sure that those data are going to be out and demonstrate that our vaccines will work," she said.

Second, Walensky said the CDC needs to evaluate data on whether vaccinated people might possibly be getting infected but not showing symptoms, and could unknowingly transmit the virus to others.

"We have to make sure that it does not lead to asymptomatic transmission -- that people are not able to get the disease and give it to somebody else, even if they don't have symptoms -- that was not measured in the clinical trial," she said.

"It is all of that evolving science that is going into our decisions about when to lift the mask mandates for vaccinated people," she added.

White House Covid-19 senior adviser Andy Slavitt has said that the CDC needed to move cautiously.

"If you are the CDC, the cost of a misstep, the cost of going too fast and having to go backwards, is you lose everybody in the process," Slavitt told CNN on April 27.

On Sunday, Dr. Anthony Fauci, President Joe Biden's senior medical adviser, seemed to signal that it's time for CDC to loosen up some of its requirements.

When asked on ABC News whether it is time to start relaxing indoor masks requirements, Fauci said, "I think so, and I think you're going to probably be seeing that as we go along, and as more people get vaccinated."

The CDC will be updating its guidance almost in real time, as more Americans get vaccinated, said Fauci,who is director of the National Institute of Allergy and Infectious Diseases.

"We do need to start being more liberal, as we get more people vaccinated," he added.

However, multiple sources familiar with the deliberations have told CNN that the CDC is not expected to issue new guidance for fully vaccinated people this week.

One of the federal officials interviewed by CNN noted that some at CDC recognize that the agency needs to move faster to update guidelines.

"[The CDC] is definitely not nimble," the official said, noting that many CDC experts have to review every piece of guidance. "It's a long process."