By ZEKE MILLER and JONATHAN LEMIRE Associated Press\r\n\r\nBETHESDA, Md. (AP) \u2014 President Joe Biden said Thursday that the U.S. will have enough supply of the COVID-19 vaccine by the end of the summer to inoculate 300 million Americans.\r\n\r\nBiden made the announcement at the sprawling National Institutes of Health complex just outside Washington as he visited some of the nation's leading scientists on the frontlines of the fight against the disease. He toured the Viral Pathogenesis Laboratory that created the COVID-19 vaccine now manufactured by Moderna and being rolled out in the U.S. and other countries.\r\n\r\nThe U.S. is on pace to exceed Biden's goal of administering 100 million vaccine doses in his first 100 days in office, with more than 26 million shots delivered in his first three weeks.\r\n\r\n"That's just the floor," Biden said. "Our end goal is beating COVID-19."\r\n\r\nBiden announced on Thursday that the U.S. had secured contractual commitments from Moderna and Pfizer to deliver the 600 million doses of vaccine by the end of July \u2014 more than a month earlier than initially anticipated.\r\n\r\n"We're now on track to have enough supply for 300 million Americans by the end of July," he announced.\r\n\r\nThe pace of injections could increase further if a third coronavirus vaccine from drugmaker Johnson & Johnson receives approval from the Food and Drug Administration.\r\n\r\nSpeaking with Dr. Anthony Fauci, the nation's top infectious-disease specialist, Biden emphasized that his administration is doing everything possible to increase the vaccine supply and the country's capacity to deliver injections into arms.\r\n\r\n"It's been a hell of a learning process," Biden said.\r\n\r\nBiden, wearing a mask, used his remarks to criticize President Donald Trump, saying he inherited "no plan to vaccinate most of the country."\r\n\r\n"It is no secret that the vaccination program was in much worse shape than my team and I anticipated," he said.\r\n\r\nTo date, the Biden administration has deployed active-duty troops to help stand up mass vaccination sites in several states, as it looks to lay the groundwork for increasing the rate of vaccinations once more supply is available.\r\n\r\nThe Viral Pathogenesis Laboratory is led by Dr. Barney Graham, whose team made critical discoveries years ago that laid the groundwork for rapid development of that and other COVID-19 vaccines. Before the pandemic erupted, one of Graham's research fellows, Dr. Kizzmekia Corbett, had been using those earlier findings to develop a vaccine for MERS, a cousin of COVID-19.\r\n\r\nOn the tour, Biden was shown the lab bench where researchers sequenced the virus and developed the precursor of the Moderna vaccine.\r\n\r\nArmed with their prior research, Corbett and Graham had a head start when Chinese scientists shared the genetic map of the new coronavirus in January 2020. They already knew how to make spike proteins, which coat the surface of the new coronavirus and its MERS relative, that were stable enough to be used as a key vaccine ingredient.\r\n\r\nWithin days, the NIH had sent instructions to Moderna to brew up doses, and Corbett and her colleagues were setting up the key lab and animal tests that would eventually prove they were on the right track.\r\n\r\n___\r\n\r\nAssociated Press Medical Writer Lauran Neergaard in Washington contributed to this report.