Moderna Inc. on Thursday cut its 2021 sales forecast for its COVID-19 vaccine by as much as $5 billion, as it struggles to ramp up production of its two-dose inoculation, sending its shares down nearly 11% in premarket trading.

The company's sales target cut is in sharp contrast to that of larger rival Pfizer Inc., which earlier this week raised its sales forecast for its shot.

Moderna's deliveries have been uneven as the company and its contract manufacturers strive to expand production and bottling of the shots to meet unprecedented demand from countries.

The vaccine-maker said it was seeing a temporary impact from the expansion of bottling capacity, also known as fill/finish, and that longer lead times for international shipments would push some deliveries to early 2022.

Moderna said it was now expecting sales of between $15 billion and $18 billion from $20 billion estimated previously.

The cut in sales forecast was also due to the prioritization of deliveries to low-income countries.

Roughly 10% of the vaccine's total supply is expected to go to low-income nations, Chief Executive Officer Stéphane Bancel said.

Deliveries were pegged between 700 million and 800 million doses for the year. Moderna has said it expects to make 800 million to 1 billion doses in 2021.

The COVID-19 vaccine brought in sales of $4.8 billion in the third quarter. Analysts had expected sales of $5.86 billion, according to five analysts polled by Refinitiv.

Still, Moderna said its sales could be in the range of $17 billion to $22 billion next year as it signs deals with more countries for its vaccines and booster doses.