The Trump administration will start releasing more doses of the Pfizer and Moderna COVID-19 vaccines to states immediate instead of holding back the second dose, as Health and Human Services Secretary Alex Azar says states should expand vaccinations to everyone age 65 and older in an effort to get the vaccine to more people immediately.

President-Elect Biden has called for similar changes to the COVID-19 vaccine rollout. Biden is expected to announce more details about his plans later this week.

Azar said the changes move the country to the next phase of the COVID-19 vaccine rollout, saying the administration is confident in the supply from manufacturers and there have already been more doses sent to states than health care workers and people in long term care facilities eligible for the first phase of doses.

“This is just a staging, moving to the next phase on the vaccine program,” Azar said. “We’ve had so much success with quality and predictable manufacturing and almost flawless distribution of the vaccine, but we have seen now that the administration in the states has been too narrowly focused,” he said on “Good Morning America.”

He went on to say that states should not be waiting until all health care workers and long term care residents in Phase 1a are vaccinated to move on to other vulnerable populations, comparing it to not waiting until all members of a group are boarded to continue boarding an airplane. Azar said it will be easier to manage eligibility based on age as vaccinations expand to pharmacies and more sites.

Releasing second doses marks a change from the administration’s plan to earmark second doses for people vaccinated in the early phases of the process to ensure there would be enough doses available when it was time for their second dose. Gen. Gustav Perna said in November that plan was expected to change when there was sufficient production of authorized vaccines that officials were no longer concerned about being able to provide second doses.

A Moderna spokesperson tells ABC that the administration has visibility into its supply and therefore it should be “no problem for government agencies to anticipate and plan second doses per our schedule.” Moderna says it’s on track to supply a total of 100 million doses to the U.S. by the end of March.

The changes come amid public frustration about the pace of vaccinations and confusion about the process of who is eligible and limited number of appointments available to be vaccinated. It will ultimately be up to governors and state and local officials to decide who is eligible to receive the vaccine in their state based on if they have enough supply of vaccine doses to meet demand and vaccinate the most vulnerable populations and essential workers.

Azar said he would rather have people working to get appointments for vaccination than vaccines sitting in freezers unused.

Experts say it is critically important to ramp up vaccinations to protect more Americans amid record high numbers of new COVID-19 cases, hospitalizations, and deaths, and new, possibly more contagious variants of the virus that causes the disease detected in the U.S.

Centers for Disease Control Director Robert Redfield said it’s especially important to vaccinate people vulnerable to severe illness from COVID-19 as hospitals around the country continue to be overwhelmed.

“We believe it’s critically important at this time to get those vulnerable people as quickly as we can” to maintain hospital resilience, Redfield said during a briefing with Operation Warp Speed.

As states speed up who is eligible to receive the vaccine, which many have already done, they’ll like see a tidal wave of demand from people trying to book a limited number of slots for the doses of vaccine available to be given out on a day to day basis. Some experts say making more doses of the vaccine available won’t resolve all the problems in the rollout if local efforts to administer the vaccine don’t get more support and staff to carry it out.

Dr. John Brownstein, chief innovation officer at Boston Children’s Hospital and Harvard University professor, said releasing more doses could probably help increase vaccinations but there’s still a “last mile challenge” to get the vaccine to the people who need it.

“It’s not just about releasing the doses, it’s about the logistics. So the states are going to have to keep working out the kinks, identifying priority groups, building networks of providers, and I think the big issue we’re probably not talking about enough is the logistics in how do you find out if you’re eligible. It’s really confusing. Every location has a slightly different eligibility, and then you have to find a confusing website, maybe book an appointment and deal with long lines,” Brownstein, an ABC News contributor, told ABC News Live.

“So there’s a lot of issues with that last mile we still have to deal with regardless if we release those second doses.”

Azar said the administration is willing to “deploy teams to help states doing mass vaccination efforts if they wish to do so,” saying the distribution has been too centered around hospitals and more mass vaccination sites could help speed things up.

Federal officials are not recommending a change in how the COVID-19 vaccines are administered, including that both the Pfizer and Moderna and vaccines require two doses administered 21 or 28 days after the first. The Food and Drug Administration has said there is not evidence to support changing that regimen and that it is important everyone vaccinated receives the second dose of the same vaccine on time to ensure they remain effective.

Biden said last week he wants to set up more federal vaccination sites or mobile clinics to reach more rural areas. HHS and Operation Warp Speed are also moving up the timeline to get more doses of the vaccine to local pharmacies and health clinics.

The pace of vaccinations has increased in recent weeks – almost 9 million people have received their first dose according to CDC data – but experts say the pace needs to speed up even more and that state and local jurisdictions need more resources and support to resolve the bottleneck.

If governors follow federal officials’ calls to expand eligibility millions more people could be vaccinated earlier than anticipated. The CDC says there are 21 million people over the age of 75 in the country and 32 million people between the age of 65 and 74. 56% of adults also have a medical condition that could make them eligible to receive the vaccine immediately under the new recommendations regardless of age, including cancer, COPD, heart conditions, obesity, diabetes, or a compromised immune system.