By Maria Armental

Pfizer Inc. Chief Executive Albert Bourla said the company ramped up production of its Covid-19 vaccine and will be able to deliver 10% more doses to the U.S. by the end of May than previously agreed.

In addition, Mr. Bourla said on Twitter, Pfizer will supply the full 300 million doses agreed on for the end of July two weeks early.

"In the fight against COVID-19, we're in this together," he tweeted Tuesday.

Moderna Inc. on Tuesday said it remained on track to deliver the second 100 million doses to the U.S. government by the end of May and another 100 million doses by the end of July.

The supply chain outside of the U.S. was established approximately one quarter behind the U.S. supply chain and continues to ramp up, Moderna said.

On Tuesday, U.S. health authorities recommended pausing the use of Johnson & Johnson's Covid-19 vaccine to look into reports of rare but severe cases of blood clots.

J&J's vaccine uses similar technology as a vaccine from AstraZeneca PLC and the University of Oxford, which hasn't been authorized in the U.S. and has also been linked to rare cases of blood clots.

The U.S. has an abundant supply of the Pfizer-BioNTech and Moderna vaccines, a Health and Human Services Department official said.

-- Peter Loftus and Thomas M. Burton contributed to this story.

Write to Maria Armental at maria.armental@wsj.com

(END) Dow Jones Newswires

04-13-21 1708ET