• Pfizer shares fell Thursday after a report said the U.S. drugmaker expects to ship half of the Covid-19 vaccines it originally planned for this year due to supply-chain problems.
• The company has repeatedly said publicly that it planned to ship 50 million vaccine doses this year and up to 1.3 billion doses by the end of 2021.
• In a statement Thursday, it said it was "confident" it could hit that target.

Pfizer shares fell Thursday after a report said the U.S. drugmaker expects to ship half of the Covid-19 vaccines it originally planned for this year due to supply-chain problems.

The Wall Street Journal, citing a person directly involved in the development, said some early batches of the raw materials needed for the vaccine failed to meet standards. Pfizer now plans to ship 50 million vaccines by the end of the year, down from the original 100 million it had hoped to send out, according to the Journal.

"There are several factors which have impacted the number of doses estimated to be available in 2020," Pfizer said in a statement. "For one, scaling up a vaccine at this pace is unprecedented, and we have made significant progress as we have moved forward in the unknown."

The company has repeatedly said publicly that it planned to ship 50 million vaccine doses this year and up to 1.3 billion doses by the end of 2021. Still, Pfizer shares fell more than 2% in intraday trading Thursday before closing down more than 1% after the report published. In extended trading, the stock, which has a market value of $223 billion, was down less than 1%.

The report also caused sparked a late-day sell-off in the broader market.

Pfizer said Thursday, the scale up of the raw material supply chain took longer than expected. It also was delayed by the efforts it was making to produce vaccines for clinical trials. The company said its full scale production lines in the U.S. and Europe are now complete and it is "confident" it will be able to supply the targeted doses.

Vaccines can contain preservatives to prevent contamination, sterile water, genetic material of the virus and other ingredients, according to the Centers for Disease Control and Prevention.

Pfizer, which has been working alongside German drugmaker BioNTech, applied for an emergency use authorization from the Food and Drug Administration for their coronavirus vaccine on Nov. 20. Its vaccine uses messenger RNA, or mRNA, technology. It's a new approach to vaccines that uses genetic material to provoke an immune response.

Pfizer's vaccine requires a storage temperature of minus 94 degrees Fahrenheit. By comparison, Moderna has said its vaccine remains stable at 36 to 46 degrees Fahrenheit, the temperature of a standard home or medical refrigerator, for up to 30 days. It can be stored for up to six months at negative 4 degrees Fahrenheit.

The Federal Aviation Administration said it supported the "first mass air shipment" of vaccines last week. The company plans to ship frozen vials of the vaccine to vaccination points from its sites in Kalamazoo, Michigan, and Puurs, Belgium.

Pfizer announced on July 22 that the U.S. agreed to buy 100 million doses of its vaccine for up to $1.95 billion. The agreement, part of the Trump administration's vaccine program Operation Warp Speed, allows the U.S. to acquire an additional 500 million vaccine doses

On Wednesday, the U.K. authorized Pfizer's vaccine, becoming the first country to do so.