Top US health officials reportedly say it could take at least 2 months of research before the FDA would sign off on giving people half-doses of a COVID-19 shot

• Officials are looking into whether Moderna's COVID-19 vaccine can be given out in half-volume doses, but the research could take two months, the The New York Times reported.
• After data is collected, any dosing changes would then have to be approved by the FDA.
• Operation Warp Speed head Dr. Moncef Slaoui had previously said that Moderna and the FDA were already in talks to discuss giving people half-doses, which would double the supply of available doses.
• The practice isn't currently supported by adequate scientific evidence, the FDA warned, and "may ultimately be counterproductive to public health."

It could take two months for US health officials to determine whether Moderna's COVID-19 vaccine can be given out in half-volume doses, the The New York Times reported Tuesday.

This comes as the US, which has authorized two coronavirus vaccines for emergency use, continues to face criticism for its slow vaccine rollout.

Scientists at the National Institutes of Health, Operation Warp Speed, and Moderna are looking at the effects of doubling the drugmakers vaccine supply by injecting people with half-doses, Dr. John R. Mascola, director of the NIH's Vaccine Research Center, told the Times.

"The total supply of vaccine has always been a concern," Mascola said. "It's important to do these analyses that we're doing, and have all that data in our pocket in the event that there's a need to use it."

Read more: Inside Moderna's historic coronavirus vaccine program that transformed the biotech upstart into a $55 billion drug industry powerhouse

This followed comments made by Operation Warp Speed head Dr. Moncef Slaoui on CBS on Sunday that Moderna and the US Food and Drug Administration (FDA) were already in talks to discuss giving people half-doses.

Giving out half-doses of Moderna's vaccine would induce an "identical immune response" to the 100-microgram dose in people ages 18 to 55, Slaoui had said, citing data from Moderna's clinical trials.

Mascola and Dr. Anthony Fauci, the US's leading infectious disease expert, confirmed this research to the NYT, but the FDA issued a statement Monday urging against the practice.

The agency warned healthcare providers not to halve doses, mix and match shots, or widen the window between the doses' delivery. The practice isn't currently supported by adequate scientific evidence, it said, and "may ultimately be counterproductive to public health."

"Without appropriate data supporting such changes in vaccine administration, we run a significant risk of placing public health at risk," it added.

Read more: COVID-19 vaccine makers are scrambling to fill 5,000 vacancies as more countries approve the shots. One is even offering $3,000 sign-on bonuses for night-shift workers.

The early phase 2 clinical trial Slaoui based his argument on only involved 600 people and was conducted to test for immune response, not the vaccine's effectiveness, Fauci told the NYT. The Phase 3 trial, which showed that the vaccine was 94% effective, was only based on the 100-microgram dose.

The FDA would have to approve any changes to the doses, Mascola said. Before it would be able to do this, researchers would need to present the agency with data on blood samples from the Phase 3 trial's participants and potentially also data from a new Phase 2 trial of 50-microgram doses.

Speaking to CBS Sunday, Slaoui described the idea as a "more responsible approach" than adopting the UK's strategy of giving out as many initial full doses of the vaccine as possible.

UK officials said in late December they would prioritize getting people their first doses of coronavirus vaccines instead of holding enough to ensure everyone could get a second dose in the recommended amount of time. The country is now allowing up to 12 weeks to pass between doses. Scientists are split on the untested strategy.

Read more: New York hospitals could be fined $100,000 and lose access to future COVID-19 vaccine doses if they don't use up their supplies within a week, Cuomo says

Though the rollout of the two vaccines authorized for emergency use in the US had a slow start, public-health officials have expressed optimism that this could pick up speed.

"We are not where we want to be, there's no doubt about that, but I think we can get there if we really accelerate, get some momentum going, and see what happens as we get into the first couple of weeks of January," Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, told ABC News earlier this month.

President-elect Joe Biden, who will be sworn in on January 20, plans to vaccinate 100 million people in his first 100 days in office, though he noted that it would take "years, not months," to vaccinate all Americans at the current rate.

As of Thursday morning, almost 6 million Americans had received their first dose of either Pfizer-BioNTech or Moderna's COVID-19 vaccine, per CDC data. Operation Warp Speed had aimed to administer the first doses to 20 million people by the end of December.