(The Hill) — A nationwide shortage of infant formula is worsening, sending parents scrambling and lawmakers demanding answers. 

For the week starting April 24, the out-of-stock percentage of formula reached 40%, according to an analysis by Datasembly, a retail tracking company. That’s an increase from 31% at the beginning of April.

In the beginning of May, the nationwide out-of-stock percentage grew even more, and stands at 43% for the week ending May 8th, the company said.

Healthy babies have plenty of options for feeding, but the shortages are being felt most acutely by parents whose children need specialty formula to survive because they suffer from severe medical conditions, including metabolic disorders. 

Supply chain problems have been exacerbated by a nationwide recall of formula made by Abbott Nutrition, one of the largest formula suppliers in the country, and the continued shutdown of Abbott’s manufacturing plant in Michigan.

The Food and Drug Administration (FDA) launched an inspection of the plant amid complaints that four infants had been hospitalized with rare bacterial infections after consuming powdered formula that was made in the facility. Two infants died from the infections.

Abbott and the FDA issued a recall of three brands of formula made in the facility, including Similac.

The issue exploded politically, as Republicans tried to blame the Biden administration for the shortage.

“This is absolutely UNACCEPTABLE in America,” Rep. Elise Stefanik (R-N.Y.) tweeted. “Sadly, this has become the norm because of Joe Biden’s radical agenda.”

In a letter to FDA commissioner Robert Califf on Tuesday, Stefanik blamed Biden’s “inflationary policies” for the shortage. 

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White House press secretary Jen Psaki on Monday said FDA is working “around the clock” to fix the shortage, but noted there is no national stockpile of formula the administration could tap to alleviate the issue.

“The FDA issued a recall to make sure that they’re meeting their obligation to protect the health of Americans — including babies who, of course, were receiving or taking this formula — and ensure safe products are available. That’s their job,” Psaki said.

Lawmakers have been pressing the agency for specifics on the investigation and when Abbott’s plant will be allowed to reopen. 

Last month, Sens. Bob Casey (D-Penn.) and Sherrod Brown (D-Ohio) asked Califf for an update into the investigation, but have not yet received a response.

In a letter sent to the FDA and the U.S Department of Agriculture on Tuesday, Sen. Mitt Romney (R-Utah) said he was concerned about the “apparent lack of an effective mitigation strategy.”

Romney’s letter raised questions about the vigor of FDA’s inspection process and how quickly the agency responds to consumer complaints.

“In its attempt to balance safety from contaminated product and safe infant development through formula access, FDA is achieving neither objective,” Romney wrote.

“I am alarmed to see documented instances of non-descript contamination in September 24, 2021, and inadequate sample testing to prove formula products met microbiological quality standards in 2019,” Romney wrote. “This documentation suggests FDA’s routine inspection authority is insufficient to meet consumer safety demands, yet its hammer of near-shutdowns of facilities causes a ripple effect throughout the country.”

In a separate letter, Sen. Chuck Grassley (R-Iowa) also asked if the agency has plans to modify its investigation procedures to ensure that future shortages can be avoided.

The agency on Tuesday outlined additional steps it was taking to mitigate the shortages, including allowing Abbott to release certain specialty products on a case-by-case basis.

But FDA did not give a timeframe for when Abbott’s facility would reopen. 

The agency noted that other infant formula manufacturers “are meeting or exceeding capacity levels to meet current demand.”

“We recognize that many consumers have been unable to access infant formula and critical medical foods they are accustomed to using and are frustrated by their inability to do so. We are doing everything in our power to ensure there is adequate product available where and when they need it,” Califf said in a statement. 

But it’s not immediately clear if the manufacturers can meet that demand.

“We’ve received assurances from manufacturers they’re going to ramp up production, but that has not yet translated to increased stock on the shelves,” Brian Dittmeier, senior director of public policy for the National Women, Infants and Children Association, said in a CNN interview Tuesday.