(CNN) -- Dr. Anthony Fauci, the nation's top infectious disease expert, on Sunday urged Americans to take any of the three "highly efficacious" coronavirus vaccines now available to them and not delay getting one vaccine over another.
His comments come after the US Food and Drug Administration on Saturday authorized Johnson & Johnson's COVID-19 vaccine, adding a third vaccine option for Americans.
"These are three highly efficacious vaccines. I can tell you I have been fully vaccinated with one that was available. It was the Moderna," he told CNN's Dana Bash on "State of the Union." "If I were not vaccinated now and I had a choice of getting a J&J vaccine now or waiting for another vaccine, I would take whatever vaccine would be available to me as quickly as possible for the simple reason of what I said a moment ago, we want to get as many people vaccinated as quickly and expeditiously as possible."
The Johnson & Johnson vaccine is the first single dose COVID-19 vaccine available in the US and is considered 72% effective specifically for the US and offered 86% protection against severe forms of the disease in the country. The vaccine was tested in more than 44,000 people in the US, South Africa and Latin America. Globally, it was 66.1% effective against moderate to severe/critical COVID-19 at least four weeks after vaccination, according to an FDA analysis.
But while Fauci and health experts have touted the vaccine's efficacy against the virus, there is some concern among Americans about its efficacy compared to vaccines from Pfizer and Moderna that are about 95% protective.
"You can understand that type of a concern, but in order to really compare vaccines, you have to compare them head-to-head and these were not compared head-to-head," Fauci told Bash.
And while the initial supply of the Johnson & Johnson vaccine is limited -- the company says it only has about 4 million doses of its vaccine ready to ship "immediately" -- it should have 20 million ready by the end of March.
The US Centers for Disease Control and Prevention Advisory Committee on Immunization Practices, known as ACIP, will meet on Sunday to set the guidelines for who should get the vaccine. Their vote is scheduled for 3 p.m. ET.
Vaccines and variants
The J&J vaccine comes as new variants of COVID-19 are circulating in the US, one of them in New York City, that is concerning researchers.
Researchers had told the VRBPAC committee that the Johnson & Johnson vaccine was tested at a different time -- when more virus was circulating and after new variants had arisen that have the ability to evade some of the immune response. Although they were not able to show that these variants were responsible for the apparent lower efficacy of Johnson & Johnson's vaccine, they told the committee it could have been a factor.
Viruses mutate all the time. The more people who are infected, and the longer they are infected, the more chance the viruses have to change. But sometimes a mutation or pattern of mutations takes hold and gets passed along. If viruses with such patterns become more common, they're called variants.
Fauci said Sunday the variants should be taken seriously and the best way to address the variants is to not only continue public health measures, but to also vaccinate as many people as possible "because even when you have variants, the vaccines will be important in preventing the spread."
"You get variants when the virus has sort of like a complete field of going wherever it wants to go because the people are vulnerable. If you prevent that by public health measures and vaccination, you'll dampen the effect of these variants," he said.
This story has been updated with additional developments.
CNN's Jen Christensen, Christina Maxouris and Maggie Fox contributed to this report.