Watch live: Senate holds hearing on Trump administration's Operation Warp Speed to develop coronavirus vaccine

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The U.S. Senate Appropriations Subcommittee on Labor, Health and Human Services, Education, and Related Agencies is holding a hearing Thursday on "Operation Warp Speed," the Trump administration's plan to rush development on a safe and effective coronavirus vaccine. 

Dr. Robert Redfield, director of Centers for Disease Control and Prevention, is scheduled to testify along with Dr. Francis Collins, director of the National Institutes of Health, and Dr. Gary Disbrow, acting director of the Biomedical Advanced Research and Development Authority's office of the assistant secretary for preparedness and response.

The hearing comes as several pharmaceutical and biotech companies such as Pfizer, BioNTech and Moderna are in the process of developing an experimental Covid-19 vaccine. 

Pfizer released positive results Wednesday from its closely watched early-stage human trial of its vaccine. The company's working alongside with the German drugmaker BioNTech. 

Pfizer said one of its four coronavirus vaccine candidates produced neutralizing antibodies, which researchers believe is necessary to build immunity to the virus, in all participants who received two of the 10 or 30 microgram doses after 28 days, according to the preliminary data. 

The drug giant said the vaccine was generally well tolerated, though the experimental vaccine caused fever in some patients, especially for those who were in the 100 microgram group.

Another leading vaccine candidate Moderna is expected to enter a late-stage trial later this month. If all goes well in Moderna's next trial, its vaccine could be available for public distribution by the end of the year. 

Scientists hope to get a vaccine to market soon but are setting expectations low for how quickly it can happen. 

Dr. Anthony Fauci, the nation's leading infectious disease expert, has said he is "cautiously optimistic" scientists can find a safe and effective vaccine by early 2021. 

— CNBC's Berkeley Lovelace Jr. contributed to this report.

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