Public health experts say while a vaccine against the novel coronavirus might be available to some Americans in early 2021, it likely will be a while longer before a coronavirus vaccine is available for U.S. children.

A vaccine approval is coming. Get ready to ask these 8 questions.

Why a vaccine for children may take a while

Children's immune systems often respond differently to vaccines than adults' immune systems, the New York Times reports, and immune system responses can even vary among children of different ages. As a result, different research is needed to evaluate whether a coronavirus vaccine candidate is effective and safe in children. And currently, none of the major clinical trials evaluating experimental coronavirus vaccines include children, Axios reports.

That means drugmakers and federal regulators may not have the data needed to properly evaluate coronavirus vaccine candidates for children for some time.

"We don't know if it's safe, or how kids will respond to it, so I can't say next year that they definitely should get it," Rhea Boyd, a pediatrician and public health advocate, said. "I don't think we would require it in a year from now, and maybe not in five years from now."

Further, because data suggest that children are less likely to develop a serious case of or die from Covid-19, standards for adverse side effects associated with a coronavirus vaccine likely will be high, the Times reports.

Barry Bloom, an immunologist at the Harvard T.H. Chan School of Public Health, said he thinks it would be best for drugmakers to complete their coronavirus vaccine clinical trial in adults before focusing on children, because results from the adult trials may shed light on which candidates could be safest for children. Once drugmakers have that data, they should begin conducted trials focused on children in areas of the country that typically have good record-keeping on childhood vaccinations, Bloom said.

A difficult balance

Ultimately, drugmakers and federal regulators face the difficult task of achieving the right balance between quickly identifying a coronavirus vaccine for children and ensuring the public trusts that there has been adequate data to show a coronavirus vaccine for children is effective and safe, according to Axios. If a vaccine is available too quickly, people may question how safe it is, Axios reports.

On the other hand, if it takes too long, it may be even harder for the United States to curb its coronavirus epidemic, according to Axios. While children are less likely to develop a severe case of and die from Covid-19, they still can pass the coronavirus on to adults, who are at higher risk. That's why some experts say identifying a coronavirus vaccine for children shouldn't be delayed.

Evan Anderson, a pediatric infectious disease specialist at Emory University, said clinical trials on coronavirus vaccine candidates should include children as soon as possible, with an aim the of having children vaccinated before the start of the 2021 school year.

"We owe it to our children not to delay moving forward with initial studies to evaluate promising vaccine candidates," he said.

And John Moore, a professor of immunobiology at Weill Cornell Medical College, said vaccinating children against the novel coronavirus "will reduce community spread and protect adults, so it's more of a herd immunity rather than a specific immunity question. If you need 70% protection in herd immunity, at some point you will need to include children in that."

For their part, some drugmakers have made plans to soon begin including children in their coronavirus vaccine trials.

Pfizer, for example, has lowered the age minimum for its coronavirus vaccine clinical trials to 16—and according to Pfizer spokesperson Steven Danehy, the company intends to work with regulators to plan a study on its vaccine candidate's effects in younger children.

"The earlier we can understand the safety and efficacy of this population, the sooner they will be able to receive our potential vaccine, if approved, and the sooner we will be able to determine if the vaccination of children could prove an important public health strategy to prevent spread of [the new coronavirus]," Danehy said.

Similarly, Moderna said it is preparing to test its coronavirus vaccine candidate in children. "Now that Moderna has sufficient safety data in adults, we plan to be starting pediatric trials in the near future, subject to regulatory approval," the company said.

Overall, Rick Kennedy, who studies immune response development after vaccinations at the Mayo Clinic, told Axios, "I think they'll try to come up with a compromise that gives them some safety information in the minimal amount of time possible" (Weintraub, USA Today, 9/24; Castronuovo, The Hill, 9/24; Owens/Primack, Axios, 9/28; Nierenberg/Blum, New York Times, 9/23).