COVID-19 vaccine testing on children: What scientists want you to know

Though Dr. Anthony Fauci, the White House chief medical adviser, predicted a COVID-19 vaccine may not be available for high schoolers until the fall and for younger kids until early next year, scientists and vaccine makers say studies are moving as quickly as possible to ensure the vaccines are safe and effective for the nation's children.

Pfizer and Moderna are in the midst of testing their vaccines in children and teen ages 12 to 15 and 12 to 17, respectively, and both companies expect to have data by June. Next, the companies will start testing their vaccines in progressively younger ages groups. Currently, the Pfizer-BioNTech vaccine is authorized for persons 16 and older, and Moderna's vaccine is authorized for those 18 and older.

Experts say it's crucial to test vaccines in children through carefully designed studies. Children are not simply smaller adults, meaning it's not safe to assume that any drug or vaccine that works well for adults will also be highly safe and effective in children.

According to the Centers for Disease Control and Prevention, over 3.1 million children have tested positive for COVID-19, and more than 240 have died.

Studies for children look similar to those for adults, but with some key differences. Like adult studies, half of the children participants receive an injection with the vaccine, and the second half of the participants receive a saline placebo injection.

However, unlike adult vaccine trials, researchers won't have to enroll tens of thousands of volunteers and wait for some to become infected as they go about their daily lives. Instead, they enroll a few thousand volunteers and analyze their blood to ensure the vaccine is doing its job of provoking an appropriate immune system response.

That means experts predict the trials will progress faster than those for adults. It likely take a few weeks, rather than months, to see results.

"We are looking mostly for safety and immune responses generated, which correlates with vaccine effectiveness over large numbers," said Dr. Todd Ellerin, an ABC News contributor and infectious disease specialist at South Shore Health.

The immune responses in children will be compared to the immune responses generated in adults following vaccination.

"In general, kids have an equal or greater immune response compared to adults," Ellerin said.

The way COVID-19 vaccines are being tested in children mirrors the way other vaccines have been tested in children in the past, with researchers monitoring for any new safety concerns in children.

"Clinical outcome data will still be collected, but these trials are primarily concerned with adverse events and immune (or antibody) responses," said Dr. Michael Chang, a pediatric infectious disease specialist with McGovern Medical School at UTHealth in Houston.

Although children need parental consent to volunteer, they can leave the study any time they wish, just like adults, according to Dr. Robert Frenck, lead investigator of the COVID-19 vaccine trials at Cincinnati Children's Hospital.

Experts say it is crucial to vaccinate children not just to protect them, but to stop the spread of disease. Children tend to have mild or no symptoms but could transfer the virus to their older loved ones at home.

"If you wipe out the infection in the younger children, they don't spread it to the adults, and so then, you can get a big handle on disease just by targeting the younger children and getting the infection out of that age group," Frenck said.

Because children comprise nearly a quarter of the overall U.S. population, experts say vaccinating children will be crucial to reaching herd immunity -- that is, the moment when so many Americans are immune that the virus has nowhere left to go.

Raehannah Jamshidi, M.D., Ph.D., a pediatric resident with McGovern Medical School at UTHealth in Houston, is a contributor to the ABC News Medical Unit.