A new report suggests U.S. drug giant Johnson & Johnson is looking more and more incapable of delivering its promised 20 million COVID-19 vaccine shots to the federal government by the end of this month.

Since the FDA approved the vaccine in late February, nearly 4.6 million of the company's shots have been shipped to state and federal vaccine services, according to Politico. While next week's tranche will be the largest increase in supply since the first week of allocations, it may not even bring the company halfway to its self-imposed goal.

Three senior administration officials have previously expressed concern over Johnson & Johnson likely to miss its goal of 20 million doses of coronavirus vaccine promised by the end of this month.

Company spokesman Jake Sargent told Politico the company "expect[s] to deliver 20 million single-shot vaccines by the end of March." However, the new production process may face technical challenges and regulatory delays.

Notably, Johnson & Johnson is shipping parts from Europe to a "fill and finish" plant in the U.S. before delivering the doses to the federal government, according to officials.

A person familiar with the process said the company is also waiting for the FDA to approve two key American partners, Emergent BioSolutions and Catalent, which will send out "tens of millions" of available shots.

The authorization is likely to be granted in the coming days, according to one source familiar with the situation, and the amount of doses issued is expected to be in the "millions," Politico reported.

Emergent has been working on Johnson & Johnson's vaccine development since early last year, and the company said in a statement that it expects to deliver 1 billion vaccines this year for J&J and AstraZeneca, another vaccine provider.

However, Emergent was not used in J&J's original emergency use application, so their doses sat unused.

The situation has frustrated administration officials, who are seeking to meet President Joe Biden's order to provide vaccines to all adults in the U.S. by May.

Jen Psaki, White House press secretary, announced Tuesday that 4 million doses are ready for delivery next week.