Dr. Anthony Fauci said on Sunday that the COVID-19 vaccine will likely be unavailable for school-age children for "months."

Fauci, Director of the National Institute of Allergy and Infectious Diseases, said the COVID-19 vaccine will have to be tested for adult use first before it could be administered to children.

He noted that the COVID-19 vaccine's performance in adults will determine for safety and effectiveness that may apply to children, reported New York Post.

(Photo : Tasos Katopodis/Getty Images) Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases look on during a White House Coronavirus Task Force press briefing in the James Brady Press Briefing Room at the White House on November 19, 2020 in Washington, DC.

As The Sun noted, some vaccine trials tried to involve children while others didn't.

For example, Pfizer did clinical trials with children of ages 12 or older while Moderna chose to only conduct trials among adults aged 18 and above.

In an interview on NBC on "Meet the Press", anchor Chuck Todd also pointed out the varying ages in trials to Fauci but specifically asked for a possible timeline and process for school-age children.

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The short answer is: It could take longer compared to adult trials. Fauci explained this further into the interview.

COVID-19 Vaccine Trials Also Required for Children

"[T]raditionally when you have a situation like a new vaccine, you want to make sure, because children as well as pregnant women, are vulnerable," Fauci told Todd.

He also explained that after a vaccine has been proven safe and effective among adults, tests can start running to determine if the same results can be replicated among children.

This is a process is called a "bridging study" which is similar to the adult trials. It process could help speed up the approval for children's use, according to Fauci.

The goal of the bridging study is to show that the COVID-19 vaccine is safe to give to children and have a "comparable immunogenicity", or the same type of immune response.

He added that the bridging process will take shorter time than a 30,000 person trial.

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Fauci projected efforts to give the vaccine to children will likely start on January "to get to the children sooner rather than later."

Choosing to hold separate trials for children may be beneficial, but some physicians call for the inclusion of children in other COVID-19 trials where possible.

"Children are not just small adults," Dr. Sallie Permar, a professor of pediatrics, microbiology and immunology at the Duke University School of Medicine, told NPR.

Permar said a child's immune system is different from that of adults, rendering some vaccine more or less effective on children.

Permar called for specific studies on the pediatric populations to make sure children are not left behind in COVID-19 vaccine research.

Some Adults Encouraged to Take COVID-19 Vaccine

Fauci also said in the NBC interview that adults who recovered from COVID-19 will likely be advised to take the vaccine.

He said since the duration of a person's COVID-19 immunity after recovery is still unknown, "it would not be surprising" even recovered adults were advised to take a vaccine.

Fauci also noted that COVID-19 vaccine trials by Moderna have some recovered patients as participants, saying these patients "gave indication" of infection in the past and good recovery from the virus.