WASHINGTON (AP) – The Trump administration opted last summer not to lock in a chance to buy millions of additional doses of one of the leading coronavirus vaccine contenders. That decision could delay the delivery of a second batch of doses until manufacturer Pfizer fulfills other international contracts. The revelation was confirmed Monday by people familiar with the matter. It came a day before President Donald Trump aimed to take credit for the speedy development of forthcoming coronavirus vaccines at a White House summit Tuesday. Pfizer’s vaccine is expected to be endorsed by a panel of Food and Drug Administration advisers as soon as this week.