Pfizer Inc. scaled back its COVID-19 production targets earlier this year after the drugmaker ran into difficulties securing all the materials it needs to produce the shots at a large scale.

In news releases through September, Pfizer had said that it aimed to manufacture up to 100 million vaccine doses this year. But in several releases in November, the company cut that to an estimate of up to 50 million doses. Pfizer is developing its vaccine with Germany-based BioNTech SE.

A Pfizer spokeswoman said in a statement Thursday that multiple factors slowed the company down, including the time it took to source large quantities of the raw materials needed to produce the shots. But the company said it has finished bringing its manufacturing up to scale and it is now producing vaccines at a rapid pace.