(CNN) The Biden administration warned Wednesday that second Covid-19 vaccine booster shots -- or a new type of vaccine, if needed -- will not be free and readily available to the general public, if and when they are authorized, without additional funding from Congress.
There will, however, be enough supply for seniors and immunocompromised Americans.
"We do have sufficient current inventory of vaccines, both at states and pharmacies and other access points around the country and in our central inventory for fourth doses if they're called for this spring for our most vulnerable, including seniors," White House Covid-19 response coordinator Jeff Zients said in response to a question from CNN during Wednesday's briefing.
"Where we do not have sufficient doses is later in the year if the science dictates that all Americans should get a booster, or if there's a need for a new formulation of the vaccine, a variant-specific vaccine, for example, then we will not have sufficient supply," Zients added, calling the situation "completely unacceptable."
Dr. Anthony Fauci, President Joe Biden's chief medical adviser, suggested that second boosters could be authorized by the US Food and Drug Administration for the general public "toward the beginning of the fall" or "the end of the summer," though he said a second booster could be authorized for a smaller subset, "perhaps elderly" Americans, in the coming weeks.
Congress remains at a stalemate over what the White House says are urgently needed additional funds for Covid-19 response. In recent weeks, the administration has been actively pushing back on criticism from some Republican lawmakers reluctant to spend more money on coronavirus response when there is still available money from last year's Covid relief bill.
Ninety-three percent of the remaining money from the American Rescue Plan passed last year has been obligated or distributed to specific grantees or groups, including states and localities, according to a document sent by the Biden administration to lawmakers and obtained by CNN last week.
Zients said there is still sufficient supply "in the near term" for Americans who need their first dose, second dose or first booster.
Other top public health officials made similar warnings as the administration continued to urgently advocate for funding.
Fauci warned that the US "will not be able to continue to make these purchases" of monoclonal antibody treatments without continued funding.
Dr. Rochelle Walensky, director of the US Centers for Disease Control and Prevention, called continued funding "critical."
"If cases rise from the Omicron variant or any other variant, we have the tools -- vaccines, boosters, tests and therapeutics to be prepared -- but continued investment in these tools so that they are readily available when we need them remains critical," she said. "From a public health standpoint, it is critical that we continue to provide people with the tools to keep them, their families, and their communities safe."
Zients also warned that "failure to invest now will leave us with insufficient testing capacity and supply," calling the consequences of congressional inaction "severe" and "immediate."
Some of those immediate consequences that have already taken place, he said, include the "winding down" of funding to support uninsured Americans, as well as "fewer lifesaving monoclonal antibody treatments being sent to states" and "fewer treatments available for the immunocompromised."