WASHINGTON (Reuters) -Pfizer’s chief executive Albert Bourla said on Monday that the drugmaker has not yet signed an agreement with the United States on providing 100 million more coronavirus vaccine doses in 2021. Bourla told CNN in an interview that Pfizer is still negotiating with the U.S. on whether it will be able to deliver the vaccine in the second or third quarter of the year. “The U.S. government is asking (for) more. They have asked now for an additional 100 million doses from us,” Bourla said, adding that these were wanted in the second quarter of 2021. “We can provide them the additional 100 million doses, but right now most of that we can provide in the third quarter.” “The U.S. government wants them in the second quarter so are working very collaboratively with them to make sure that we can find ways to produce more or allocate the doses in the second quarter,” Bourla told CNN.