The Dow Jones Industrial Average gained 85 points, or 0.29%, to 29,969, the S&P 500 ended down 0.06% and the Nasdaq rose 0.23%.
The Wall Street Journal reported that Pfizer expects to ship half the doses it had planned after finding raw materials in early production that didn’t meet its standard.
Pfizer closed down 1.7%, while BioNtech was off 2%.
The S&P 500 and Nasdaq traded at record intraday highs during Thursday's session.
Jobless claims were lower than expected last week as companies ramped up hiring ahead of the critical holiday shopping season.
The Labor Department reported that 712,000 Americans filed for first-time jobless benefits in the week ended Nov. 28, down from a revised 787,000 claims the week earlier.
It was the first decline in initial jobless claims in three weeks.
The data were released a day after the U.S. recorded the deadliest day for Covid-19 fatalities, with more than 2,836 Americans dying from the disease, according to data compiled by Bloomberg. The number of Covid-19 patients in U.S. hospitals topped 100,000 for the first time.
The Pfizer vaccine was approved by Great Britain, but enthusiasm was dented by the realization the U.S. could be in for a very difficult winter until a vaccine is widely distributed.
The director of the Centers for Disease Control and Prevention warned that total deaths from Covid-19 could reach “close to 450,000” by February unless Americans take greater precautions.
“The reality is, December and January and February are going to be rough times,” said Dr. Robert Redfield, the head of the CDC. “I actually believe they’re going to be the most difficult time in the public health history of this nation.”
Los Angeles ordered residents to stay home, with Mayor Eric Garcetti warning the city was approaching a “devastating tipping point” in its fight against Covid-19.
On Wednesday, the S&P 500 posted its second straight record close after House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer called for stimulus talks to begin. Federal Reserve Chairman Jerome Powell and Treasury Secretary Steven Mnuchin urged Congress on Wednesday to approve a Covid-19 relief bill.
Senate Majority Leader Mitch McConnell said Thursday there were “hopeful signs” Congress could agree on a coronavirus relief bill before year-end.
Oil prices in the U.S. settled 0.8% higher at $45.64 on Thursday as OPEC leaders, as well as non-member allies such as Russia, reached an agreement to cut production next year more gradually than previously planned.