Ever the voice of caution through the current pandemic, Dr. Anthony Fauci on Friday dampened enthusiasm that an effective and approved coronavirus vaccine is only months away.

Instead, he said during an interview with Washington Post journalist Bob Costa on Friday, "I think as we get into 2021, several months in, that you would have vaccine that would be widely available to people in the United States."

Anthony Fauci.

Image source: National Institute of Allergy and Infectious Diseases.

Certain companies, including ambitious biotech Moderna (NASDAQ:MRNA), are making good time putting their vaccine candidates through clinical trials. Yet Fauci, the high-profile director of the National Institute of Allergy and Infectious Diseases, doubts that even efforts such as Moderna's will yield a vaccine that will go into use by the end of 2020.

"I'm a little skeptical about that, but, you know, anything is possible," he said.

Fauci's skepticism is based on the processes vaccines have to undergo before coming to market, including comprehensive testing in phase 3 trials and regulatory review. Even when the latter is fast-tracked, it can still be a cumbersome process.

Another problem is production; no matter how prepared a manufacturer might be or how efficient its manufacturing partners, it takes time to produce millions of doses of any vaccine or medication -- particularly if it is new.

On Tuesday, executives from Moderna and peer healthcare companies AstraZeneca (NYSE:AZN), Johnson & Johnson (NYSE:JNJ), and Pfizer (NYSE:PFE) testified in a Congressional hearing about their efforts in developing coronavirus vaccines. They expressed optimism that their vaccines might be ready by the end of 2020 or very early next year.