WASHINGTON, July 5 (Xinhua) - Commissioner of the US Food and Drug Administration (FDA) Stephen Hahn on Sunday refused to offer a timeline for COVID-19 vaccine, which US President Donald Trump suggested could be available "long before the end of the year."

People visit Ocean Beach during the coronavirus outbreak in San Francisco, Sunday, July 5, 2020. Californians mostly heeded warnings to stay away from beaches and other public spaces during the long weekend as state officials urged social distancing amid a spike in coronavirus infections and hospitalizations. (Photo: AP Photo)

"I can't predict when a vaccine will be available," Hahn told ABC on Sunday. "We are seeing unprecedented speed for the development of a vaccine. But ... our solemn promise to the American people is that we will make a decision based upon the data and science on a vaccine, with respect to the safety and effectiveness of that vaccine."

During a Fourth of July address in Washington on Saturday, Trump said the country is likely to have a therapeutic and/or vaccine solution long before the end of the year.

Hahn said Thursday that he was "cautiously optimistic" about current efforts to develop a coronavirus vaccine, pointing to "year's end or early next year" as potential completion dates.

More than 2,852,000 COVID-19 cases have been reported in the United States with the fatalities surpassing 129,700 as of Sunday afternoon, according to a tally by Johns Hopkins University.