The U.S. government expects to immunize 100 million people with a coronavirus vaccine by the end of March, Operation Warp Speed Chief Advisor Dr. Moncef Slaoui said on Sunday.

"Our plan from Day One has been to have a portfolio of products," Slaoui said. "Pfizer is one of them. Moderna, which is likely to be approved by Friday, probably this coming week, is able to produce 100 million doses in the first quarter, and we just announced on Friday that we're committed to acquire another 100 million doses, which will be delivered in the second quarter of 2021," Slaoui told host Chris Wallace on "Fox News Sunday."

The coronavirus vaccine developed by Pfizer (PFE  )-BioNTech (BNTX  ) was approved for emergency use in patients aged 16 and older by the U.S. Food and Drug Administration on Friday. The F.D.A. on Tuesday announced that Moderna's (MRNA  ) vaccine candidate has met all the necessary criteria for approval. The federal regulatory agency's Vaccines and Related Biological Products Advisory Committee meets Thursday to review Moderna's emergency use authorization request.

The U.S. government's unprecedented vaccine distribution plan anticipates to have about 40 million doses shipped out across the country by the end of December, that number including both vaccines developed by Pfizer-BioNTech and Moderna. Another 50 million to 80 million doses are planned to roll out in January, and other round is expected in February, Slaoui said. Both vaccines require two shots administered about a month apart to be effective at preventing severe infection.

Slaoui added that he expects that the vaccine developed by Johnson & Johnson (JNJ  ), which only requires one dose to be effective, to be ready for emergency approval by early February. The vaccine designed by AstraZeneca (AZN  )-Oxford University could be approved by the F.D.A. by February as well.

The leadership transition between the Trump administration and the incoming administration under President-elect Joe Biden is not expected to harm Operation Warp Speed's current distribution timeline.

For the U.S. to reach a level of herd immunity--which is a state where most of the population is immune, thus making it difficult for a virus to spread easily--against the coronavirus, Slaoui said that about 75% to 80% of the population will need to be vaccinated. He hopes that the nation can reach that point by May or June 2021.

The question remains whether or not enough of the American population is willing to take a coronavirus vaccine due to fears surrounding the speed at which it was developed and the potential long-term side effects that have not had enough time to surface. If only a small percentage of the population gets vaccinated, the vaccine will not do its intended job to halt the widespread coronavirus outbreak.

Slaoui encourages Americans to "listen to the data and openly agree that this is a very effective and safe vaccine."