How Will COVID Vaccine Dosages Work For Kids?

Female doctor pulling COVID-19 vaccine liquid from vial


Key Takeaways

  • The pediatric vaccine dose is still being perfected.
  • Two doses will probably be needed approximately three weeks apart.
  • It is still unknown if a booster shot will be needed.

Although scientists have determined an appropriate effective dose of COVID-19 vaccine for adults, they have yet to perfect it for children under 16. Clinical trials are underway, where researchers will assess what dosage is effective and safe in children.

Researchers are using detailed mathematical calculations and the current adult data to determine safe doses to test in children. The vaccine won't be released to the pediatric community until a safe and effective dose has been determined.

How the Dose Will Be Determined

During clinical trials in children, a variety of test doses are trialed to determine the most effective dose with the least amount of side effects.

Dr. Sharon Nachman, chief of the Division of Pediatric Infectious Diseases at Stony Brook Children's Hospital, explains that researchers use detailed mathematical formulations to determine two to three test doses for children, based on the known effective dose in adults.

“For example, if an adult got 500 milligrams, you would probably in a child test 125 and 250 and 750 milligrams, because you don't know if the kid is going to metabolize it faster or slower," she explains.

During these trials, blood samples are drawn for researchers to assess how the child's immune system has responded to each dose, how effective that dose is, and the side effects experienced by the participant.

Dr. Amina Ahmed, professor of pediatric infectious disease and immunology at Atrium Health Levine Children's Hospital, explains that there is a fine balance when finding an effective vaccine dose with minimal side effects.

“You're sort of balancing the smaller dosage in terms of side effects versus how much immune response you build as well...So you have to tinker with that dosage a little bit," she says. "You have to methodically try different doses.”

When data is available from the clinical trials featuring kids ages 12-17, research will likely expand to calculating and testing doses in younger children, and then finally infants. Exactly how fast this will happen is still unknown.

How Many Doses Children Will Need

At this stage, doses of the Pfizer vaccine (approved for age 16 and up) are likely to mimic the adult vaccination schedule. This means that two doses of the vaccine will likely be required, three weeks apart. However, testing is still underway.

Nachman points out that with other vaccine trials, such as the HPV vaccine, children needed fewer doses than adults to gain immunity. There is the potential that children may need fewer repeat doses of the COVID-19 vaccine, but it is far too early to know this yet.

Currently, the adult vaccine is about 50% effective after one dose, and 95% effective after two doses. Children in clinical trials will be given multiple doses to assess this efficacy in the pediatric population.

Nachman says, "They will do the exact same thing with children. And at the end, they'll be able to say the first dose was this protective. And the second dose was this extra protective."

How many doses they will need when the vaccine is finally released for children will depend on the effectiveness of the doses in trials.

Ahmed says that even if children do need two doses of the Pfizer vaccine, we still don’t know if a booster shot will be required at a later date.

Dr. Amina Ahmed, MD

We know we need two doses for this Pfizer vaccine to be 95% effective. We do know that. The question is, do we need repeat booster dosing?

— Dr. Amina Ahmed, MD

She says, “We know we need two doses for this Pfizer vaccine to be 95% effective. We do know that. The question is, do we need repeat booster dosing?”

Because the vaccine development has been occurring so rapidly, it is not yet known if the body's immune response will last long-term, or if, similar to other vaccines such as whooping cough, you will need a booster shot to maintain immunity.

If the Test Dose Is Too High, Will My Child Get Sick?

The COVID-19 vaccine is not a live vaccine. So if a test dose is higher than necessary during the clinical trial, it will not cause a case of COVID-19.

The body cannot get infected with COVID-19 without the full virus cell and all of its components. The vaccine only contains a portion of the virus.

Ahmed explains that the spike protein is the portion of the virus that our bodies recognize as an invading pathogen, prompting it to subsequently create antibodies. Therefore, only this portion of the virus cell is used in the vaccine.

According to the CDC, the body will take one to two weeks after the second vaccine dose to build a full immune response. After this time, if we are faced with a true case of the COVID-19 virus, the body will recognize the spike protein on the outside of the virus and start fighting off the invading cells.

Dosage Safety

Although the vaccine development for COVID-19 is moving faster than usual, safety is still paramount. This is precisely why the vaccine is not yet available for children.

According to Ahmed, it’s realistic to expect some complications in such a new development, “Do things happen? Do people have reactions? Absolutely," she says. "That happens and we're going to hear about it. But I do think that everyone is being very careful about this."

Nachman also reassures parents that the risk of incorrect dosing is extremely low. She reports that the child’s weight, liver function, kidney function, blood volume, and overall health are determined prior to dosing. These details, along with the data obtained from adults, are used to calculate safe doses to trial in children.

Dr. Sharon Nachman, MD, PhD

Because these [math] models are so sophisticated, they're almost never wrong.

— Dr. Sharon Nachman, MD, PhD

“This happens all the time in medicine, every medication that has to go into [a] kid, they practice on the math models before they ever get to the kid,” she says. “And by the time they get to the kid, because these [math] models are so sophisticated, they're almost never wrong.”

Safety data for vaccine doses in children needs to be proven before the vaccine can be released for use in the pediatric population.

Ahmed reassures parents that although the vaccines are developing quickly, safety isn't being compromised. She says, “I know people are concerned that these vaccines came out really quickly. I will...reiterate that the degree of vigilance here is max.”


The dosage examples mentioned in this article are not COVID-19 specific. They are general examples to help explain how doses are chosen for pediatric clinical trials.

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