Moderna lowered its COVID-19 vaccine sales prediction for 2021 by up to $5 billion on Thursday as it struggles to ramp up manufacturing of its two-dose inoculation, sending its shares down 11% in premarket trade.

The business said it now expects sales of $15 billion to $18 billion, down from $20 billion originally projected. Deliveries for the year were estimated to be between 700 million and 800 million doses, compared to previous expectations of 800 million to 1 billion doses in 2021.

The business highlighted lengthier lead times for overseas exports, which may now push some deliveries to 2022, as well as a temporary impact from the vaccine's expansion of bottling capacity.

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Moderna stated in August that it was "capacity constrained" for 2021 and had ceased taking orders this year.

Its output has lagged behind that of larger rival Pfizer, which anticipates COVID-19 vaccine sales of $36 billion in 2021 and another $29 billion in 2022.

Earlier this year, Moderna warned of shot shortages in the United Kingdom and Canada in the second quarter, citing an inconsistent manufacturing ramp-up.

Nonetheless, Moderna expects its sales to be in the $17 billion to $22 billion range next year as it enters contracts with more countries for its vaccines and booster doses.