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WATCH: Drug manufacturers testify on development of COVID-19 vaccines

The House Oversight and Investigations Subcommittee held a hearing July 21 on the current state of research, development, and manufacturing of potential vaccines for COVID-19, the disease caused by the novel coronavirus.

Watch the hearing in the video player above.

Officials from five drug manufacturers developing COVID-19 vaccines testified, including AstraZeneca, Johnson & Johnson, Merck, Moderna and Pfizer.

The U.S. drug manufacturers that testified at the hearing are all reportedly involved in the Trump administration’s Operation Warp Speed initiative, a national program aimed at accelerating “the development, manufacturing, and distribution” of COVID-19 countermeasures, including vaccines.

As of July 15, 2020, at least 140 COVID-19 vaccine candidates are in preclinical evaluation, and at least 23 candidates are in clinical evaluation worldwide.

Two companies recently announced promising results from their COVID-19 vaccine trials. Data from Moderna’s COVID-19 vaccine showed that it led patients to produce antibodies that can neutralize the novel coronavirus that causes the disease, though it caused minor side effects in many patients. And scientists at Oxford University said July 20 that their experimental coronavirus vaccine with drugmaker AstraZeneca has been shown in an early trial to prompt a protective immune response in hundreds of people who got the shot.

Even so, any successful COVID-19 vaccine will have to go through several rounds of research and evaluation before it is approved. Only 6 percent of candidate vaccines are ever approved for commercial use.

“When you’re dealing with vaccines, you can’t guarantee things, but you can say, based on the science and the way things are going, that I’m cautiously optimistic that we can meet that projection that we made, that I made months ago,” Dr. Anthony Fauci told the PBS NewsHour July 17. “By the end of this calendar year, and the beginning of 2021, I feel optimistic — nobody guarantees — but I feel optimistic that we will have a vaccine, one or more, that we can start distributing to people.”