Supply chain delays marred Pfizer's initial vaccine rollout plans, but the company says it will still deliver on the supply it promised the US

• The Wall Street Journal reported Pfizer cut the number of vaccines it planned to ship in 2020 due to supply chain delays.
• Sources told the WSJ that Pfizer sourced materials and set up supply chains while developing a vaccine, an "unprecedented" move.
• But Pfizer and BioNtech maintain they will produce 1.3 billion doses by the end of 2021, making up for this year's shortfall by ramping up production.
• Moncef Slaoui, the chief advisor overseeing COVID-19 vaccine distribution with the Trump administration, told CNBC's Meg Tirrell there is no change to Pfizer's vaccine commitment to the US.

Supply chain problems reportedly caused Pfizer to cut projections for its COVID-19 vaccine rollout.

Sources close to the Pfizer vaccine development told The Wall Street Journal delays scaling up raw materials, coupled with an "unprecedented" effort to deliver millions of vaccines within a year, led the company to miss target shipments.

The company said in July it would manufacture 100 million doses globally before year-end, but slashed projections to 50 million in a November 9 release.

Read more: Pfizer's top scientist tells us the pharma giant is already thinking about a new version of its coronavirus vaccine for 2021 that can overcome one of its biggest limitations

Per the WSJ, Pfizer was slow to scale up production of raw materials as it awaited results from a late-stage trial last month. Sources also said Pfizer typically would wait to source materials and set up supply chains until a vaccine gets approved. But during the COVID-19 pandemic, Pfizer began setting up supply chain in March during vaccine development, WSJ reported.

But Pfizer and BioNtech maintain they will produce 1.3 billion doses by the end of 2021, making up for this year's shortfall by ramping up production. Moncef Slaoui, the chief advisor overseeing COVID-19 vaccine distribution with the Trump administration, told CNBC's Meg Tirrell there is no change to Pfizer's vaccine commitment to the US.

Slaoui said Wednesday morning 20 million Americans would be immunized by December. Healthcare workers and nursing home residents will get initial doses, while most Americans will likely get access in mid-2021.

Operation Warp Speed launched over the summer to fast-track COVID-19 vaccine development by funding research in six promising candidates. Pfizer did not receive federal funding for its research, but used money for manufacturing and distribution.

The US Food and Drug Administration could greenlight emergency authorization for two separate vaccines, made by Pfizer and Moderna. Both of the vaccines require two doses. The companies have said they will be ready to distribute vaccines within hours of an FDA emergency authorization.

An independent advisory committee will meet on December 10 to decide on recommending Pfizer's vaccine to the FDA.

The UK has already allowed for use of Pfizer's vaccine. The WSJ reported the UK said in November that it could get 10 million Pfizer vaccine doses by year-end, but the expectation will now be four to five million.