Moderna (MRNA -3.45%) has hit a bit of a snag with the manufacturing of its COVID-19 vaccine. The company's fill-and-finish contractor, Catalent (CTLT -0.78%), is experiencing delays with some of the doses it's responsible for getting out the door. The companies didn't disclose exactly what was causing the delay.

"Fill and finish" is the last step in the manufacturing process and involves putting the vaccine into vials, slapping on labels, and other steps needed to go from a large batch of vaccine product to something healthcare workers can use. It's a relatively straightforward process but is still highly regulated by the Food and Drug Administration and agencies from other countries.

Gloved hands giving an injection into a child's shoulder.

Image source: Getty Images.

While the delay isn't ideal, Moderna has some wiggle room since it's delivered 45.4 million doses to the U.S. government, but the Centers for Disease Control and Prevention estimates only 25.5 million have been administered. The company thinks it can still hit its monthly delivery targets even with the delay at Catalent.

Moderna plans to have 100 million doses delivered by the end of March. And the biotech believes it can continue accelerating. Moderna expects to produce an average of 30 million to 35 million doses per month for February and March, which will ramp up to 40 million to 50 million doses per month from April through the end of July.

If it can hit its manufacturing targets, Moderna expects the second batch of 100 million doses will be delivered by the end of May, which was moved up from the previous goal of the end of June. The final batch of 100 million doses is expected to be delivered by the end of July.