The Centers for Disease Control waited until May 13 to lift mask recommendations in most settings for vaccinated Americans, but the science behind the decision has been known for months.

CDC Director Dr. Rochelle Walensky said the science behind dropping the agency’s stringent mask recommendations developed in just the final weeks before she announced the decision. The data on vaccine efficacy was known before that, though.

“We now have science that has really just evolved even in the last two weeks that demonstrates that these vaccines are safe,” Walensky told ABC shortly after the announcement. “They are effective, they are working in the population just as they did in the clinical trials that they are working against our variants that we have here circulating in the United States.”

ABC’s Martha Raddatz pressed Walensky on why she told the Senate two days before the restrictions were loosened that masking and social distancing should stay in place.

Walensky reportedly cited three recent studies in her decision to lift masking requirements. All three were released between late March and early May, according to Bloomberg. Those studies revealed that real-world vaccine effectiveness held up well compared to trial effectiveness, the Pfizer vaccine was effective against multiple COVID-19 variants found in the U.S. and that people who contracted COVID-19 after being vaccinated had lower viral loads and were incredibly unlikely to spread it further.

This science didn’t come about “in the last two weeks,” as Walensky said. It’s been known for months, including when Walensky was warning the public about “impending doom” from a new wave. (RELATED: Where’s The CDC Guidance For People Who Recovered From COVID-19?)

The clinical trials that led to the vaccines being approved for emergency use shows extreme efficacy in preventing death and serious illness. The CDC itself said in March that studies were confirming the real-world efficacy of the shots.

When it comes to protection against variants, studies that were released as early as January found that vaccines were effective against them, and that was the case for both Pfizer and Moderna. The assertion that scientists didn’t know whether vaccines protected against variants was never true; there was never evidence that the vaccines didn’t work against variants, despite concern from people like Dr. Anthony Fauci about the question.

Transmission was always known to be a rare issue as well. No vaccine in human history has ever had as high an efficacy rate as the coronavirus vaccines but somehow not curbed transmission. (RELATED: ‘It’s A Free-For-All’: Dana Bash Presses CDC Director On Leaving Locals To Fend For Themselves On Mask Rules)

“The experts are saying that the vaccines do not reduce transmission, but that is an inaccurate statement,” Dr. Monica Gandhi of the University of California San Francisco told the Association of American Medical Colleges in early March. “Vaccines have always decreased transmission. What they should be saying is that the clinical trials were not designed to test for asymptomatic infection, but there is every biological reason in the world to believe that they will reduce asymptomatic transmission.

The FDA confirmed that Johnson & Johnson’s vaccine substantially curbed transmission as early as February. Dr. Scott Gottlieb said there was “more and more evidence” that the vaccines stopped transmission back in February as well.

Walensky herself said in March that people who got vaccinated likely didn’t transmit COVID-19. The CDC walked back her comments, despite all of the available science generally supporting her claims.

Walensky’s current assertion that experts are only just now finding out, in mid-May, that the vaccines almost universally stop transmission, lessen symptoms and work in real-world circumstances simply is not true. (RELATED: Susan Collins Says The Golden Era Of Respect She Once Had For The CDC Is Over)

Furthermore, the CDC made no effort to update the public on which studies it was looking at to decide when to update mask guidance. It did not set any benchmarks for death rate, cases or vaccination rates to give an idea of when mandates would be lifted. It did not make note of the studies that it apparently did use when they came out, and key members of the Biden administration were reportedly left completely in the dark by the CDC decision until it was publicly announced.

Perhaps that’s why Johns Hopkins Dr. Marty Makary called this the “most political CDC in history.” It’s unclear what the deciding factor was in easing mask guidance, but based on the timeline of information, it couldn’t possibly have been just the science.