Pfizer Inc. shares declined as much as 3.1% on Thursday following a report that said the drugmaker expects to ship only half the COVID-19 vaccines this year it had initially planned.

The Wall Street Journal reported that supply-chain problems caused the New York-based drugmaker to reduce the number of vaccines it expects to ship world-wide this year from 100 million to 50 million. Pfizer is developing its vaccine with Germany-based BioNTech SE.

The two-shot vaccine, based on a technology called messenger RNA, was cleared for use by U.K. regulators this week, and has been also submitted for an emergency-use authorization from the U.S. Food and Drug Administration. A 44,000-participant clinical trial showed the shot to be 95% effective in preventing symptomatic Covid-19.

According to the Wall Street Journal, increasing output of components needed to manufacture the vaccine proved challenging last month. The drugmaker didn’t tell the Journal where the ingredient shortfalls arose.

Representatives for Pfizer didn’t immediately respond to requests for comment.

--With assistance from Riley Griffin.