US experts vow ‘no cutting corners’ as vaccine tests expand

Adm. Brett Giroir, assistant secretary of Health and Human Services, testifies during a Senate Senate Health, Education, Labor, and Pensions Committee Hearing on the federal government response to COVID-19 on Capitol Hill Wednesday, Sept. 23, 2020, in Washington. (Graeme Jennings/Pool via AP)

Dr. Stephen Hahn, commissioner of the U.S. Food and Drug Administration, testifies during a Senate Senate Health, Education, Labor, and Pensions Committee Hearing on the federal government response to COVID-19 on Capitol Hill Wednesday, Sept. 23, 2020, in Washington. (Graeme Jennings/Pool via AP)

Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, testifies during a Senate Senate Health, Education, Labor, and Pensions Committee Hearing on the federal government response to COVID-19 on Capitol Hill Wednesday, Sept. 23, 2020, in Washington. (Graeme Jennings/Pool via AP)

FILE - In this March 16, 2020, file photo, Neal Browning receives a shot at the Kaiser Permanente Washington Health Research Institute in Seattle, in the first-stage safety study clinical trial of a potential vaccine for COVID-19, the disease caused by the coronavirus. Many world leaders at this week’s virtual U.N. summit hope it will be a vaccine made available and affordable to all countries, rich and poor. But with the U.S., China and Russia opting out of a collaborative effort to develop and distribute a vaccine, and some rich nations striking deals with pharmaceutical companies to secure millions of potential doses, the U.N. pleas are plentiful but likely in vain. (AP Photo/Ted S. Warren, File)

This September 2020 photo provided by Johnson & Johnson shows a single-dose COVID-19 vaccine being developed by the company. Johnson & Johnson is beginning a huge final study to try to prove if the single-dose vaccine can protect against the coronavirus. (Cheryl Gerber/Courtesy of Johnson & Johnson via AP)

WASHINGTON — A huge international study of a COVID-19 vaccine that aims to work with just one dose is getting underway as top U.S. health officials sought Wednesday to assure a skeptical Congress and public that they can trust any shots the government ultimately approves.