WASHINGTON – The director of the Centers for Disease Control and Prevention warned Sunday that the federal government does not know how much coronavirus vaccine the nation has, a complication that adds to the already herculean task before the Biden administration.

“I can’t tell you how much vaccine we have, and if I can’t tell it to you then I can’t tell it to the governors and I can’t tell it to the state health officials,” CDC director Dr. Rochelle Walensky told “Fox News Sunday.”

“If they don’t know how much vaccine they’re getting not just this week but next week and the week after they can’t plan. They can’t figure out how many sites to roll out, they can’t figure out how many vaccinators that they need, and they can’t figure out how many appointments to make for the public,” Walensky said.

In a dig at the Trump administration, Walensky said the lack of knowledge of vaccine supply is indicative of “the challenges we’ve been left with.”

Read more: Biden surgeon general pick says U.S. racing to adapt against new Covid strains

President Joe Biden has set a goal to administer 100 million Covid-19 vaccine shots within his first 100 days. The Biden administration has been repeatedly pressed on whether that target is ambitious enough given the severity of the pandemic.

Walensky acknowledged that the U.S. must vaccinate people faster, but she said the nation faces supply constraints. Production will increase after the first 100 days, Walensky said, and the expected introduction of Johnson & Johnson’s vaccine will also help ease supply problems.

“We are really hoping that we’ll have more vaccines and that will increase the pace at which we can do the vaccinations,” Walensky said.

White House chief of staff Ron Klain said the nation also faces distribution problems because the Trump administration, which started the program, did not have a clear plan.

“The process of distributing the vaccine, particularly outside of nursing homes and hospitals, out into the community as a whole did not really exist when we came into the White House,” Klain told MSNBC’s “Meet the Press” on Sunday.

“So, the process of getting that vaccine into arms, that’s the hard process, that’s where we are behind as a country and that’s where we are focused in the Biden administration on getting that ramped up,” he added.

White House chief medical advisor Dr. Anthony Fauci, who served in the Trump administration, said Sunday the Biden target of 100 million doses in 100 days is not a final number.

“It is really a floor and not a ceiling,” Fauci told CBS’ “Face The Nation”. “It is going to be a challenge. I think it was a reasonable goal that was set. We always want to do better than the goal that you’ve set.”

Those 100 million injections will cover about 67 million people, Fauci said, some of whom will have received the required two doses while others will have received only one dose. So far, the U.S. has administered nearly 22 million doses, far below federal targets.

The need to vaccinate as many people as possible has taken on new urgency as the coronavirus mutates. Fauci said the Covid-19 vaccines currently on the market may not be as effective against new strains.

Biden’s surgeon general pick stressed on Sunday the U.S. is in a race to adapt against the new variants.

“The virus is basically telling us that it’s going to continue to change and we’ve got to be ready for it,” Dr. Vivek Murthy said during an interview with ABC News’ “This Week.”

“So the bottom line is, we’re in a race against these variants, the virus is going to change and it’s up to us to adapt and to make sure that we’re staying ahead,” Murthy said.

When asked if the U.S. is in a race against time before a Covid variant emerges that renders the vaccines ineffective, Walensky said Americans need to get inoculated when they have the opportunity and adhere to mitigation strategies to deny the virus opportunity to circulate.

“I would say we’ve been in a race all along,” Walensky said. “The more virus that is out there, the more virus that is replicating, the more likely that we are going to have mutations and variants.”