WASHINGTON (NewsNation Now) — The White House COVID-19 response team briefed the nation on the latest pandemic response efforts Monday, with the nation’s top infectious diseases expert saying second vaccine doses should not be delayed to prevent the spread of virus variants.

Dr. Anthony Fauci said while it was reasonable to think about studying the efficacy of Pfizer’s and Moderna’s vaccine as a one-dose regimen in light of supply vaccine constraints, such a study would take months to complete, thus likely making its conclusions moot. Fauci continued to encourage people get two doses of the vaccine.

The best defense against the evolution of COVID-19 and the emergence of variant strains is getting as many people vaccinated as quickly as possible, Fauci said.

Fauci said the variant of COVID-19 first found in the United Kingdom could become the “dominant” strain in U.S. by end of March, but both vaccines approved in the United States are “quite effective” against it.

Vaccines are “less so” effective on South African variant, but mass vaccinations could control the spread of the variant.

This comes after the Pentagon Friday approved the deployment of 1,100 active-duty troops to help deliver COVID-19 vaccine shots.

White House coronavirus adviser Andy Slavitt said Friday that Defense Secretary Lloyd Austin approved the Federal Emergency Management Agency’s request to “augment and expedite vaccinations across the country.”

Austin sent the first group of active-duty personnel to support state vaccination sites in California.

The 1,100 active-duty members will be split up into five teams, two from the Army, and one each from the Air Force, the Navy and the Marine Corps.

Nearly 60 million coronavirus vaccine doses have been distributed with more than 41 million doses administered, according to the Centers for Disease Control and Prevention.

President Joe Biden’s administration is also using the Defense Production Act to get Pfizer more equipment and supplies to ramp up vaccine production, according to Tim Manning, a supply chain coordinator for the nation’s COVID-19 response.

The announcements come after Johnson & Johnson asked U.S. health regulators to authorize its single-dose COVID-19 vaccine for emergency use.

The drugmaker’s application to the Food and Drug Administration follows its Jan. 29 report, in which it said the vaccine had a 66% rate of preventing infections in its large global trial.

The FDA is asking its independent advisers to publicly debate all the data behind the single-dose shot before it decides whether to green light a third vaccine option in the U.S. The panel will meet Feb. 26.

In the United States, there have been 27 million confirmed cases with more than 460,000 Americans dead from the virus, according to data complied by Johns Hopkins University.