A Moderna COVID-19 vaccine vial is held by Lincoln Community Hospital registered nurse Deanne Kahler of Hugo as she prepares to administer COVID-19 vaccinations to patients at the hospital in Hugo on Wednesday, Feb. 24 2021. (Andy Colwell, special to The Colorado Sun)

As a pediatrician specializing in infectious diseases at Children’s Hospital Colorado, Dr. Sara Saporta-Keating knows well the toll the coronavirus has had on the country’s youngest residents.

The United States has recorded more than 2.5 million cases of COVID-19 in kids ages 4 and younger, according to data presented last week to a Centers for Disease Control and Prevention advisory committee. It is the leading cause of death by infectious disease among all people ages 19 and younger. And it ranks in the top five of all causes of death for children 4 and under.

That’s what made the news that federal regulators have approved two COVID vaccines for kids 6 months to 5 years so exciting for her professionally.

But, as a parent to a 4-year-old kid? Saporta-Keating is overjoyed to be able to add another layer to her family’s pandemic protection. Her son is signed up for his first COVID shot at a clinic on Saturday.

“I’ve been waiting for this for a long time,” she said. “My husband and I are very excited.”

Now more than 27 months into the COVID-19 pandemic, vaccines are finally available for the last big age group not previously eligible. The CDC and the Food and Drug Administration have both given the go-ahead for kids to receive vaccines made by either Pfizer or Moderna. The announcement leaves only babies under 6 months old ineligible for vaccination based on age.

But the news comes with a fair number of questions. The Colorado Sun spoke with Saporta-Keating, as well as Kaiser Permanente pediatrician Dr. Hector de Leon, to find some answers.

Give me the basics. What’s the news?

After lengthy clinical trials and data review, regulators at the CDC and FDA gave emergency approval to the COVID vaccines made by Pfizer and Moderna. The federal officials made those decisions after consulting with independent advisory groups — the CDC’s advisory group includes a Colorado pediatrician, Kaiser Permanente’s Dr. Matthew Daley.

Pfizer’s vaccine is for kids ages 6 months through 4 years old. Moderna’s is for kids ages 6 months through 5 years old. But there’s nothing new in the technology. Both vaccines are just smaller-dose versions of what have been given to adults.

Both vaccines use mRNA technology — meaning they inject little bits of messenger RNA into the body with instructions for the cells to build spike proteins that resemble those of the coronavirus. That gives the body’s immune system something to practice against to prepare for a real infection.

The spike proteins can’t infect you or replicate inside you; think of it like training a security guard to recognize a burglar by showing them a picture of the burglar’s tattoo. The messenger RNA is destroyed in the process, so it doesn’t linger in the body or alter your DNA.

What is the difference between the two?

Mainly the size of the dose and the number of shots.

Pfizer opted to go for a smaller dose — 3 micrograms of mRNA, which is one-tenth of Pfizer’s adult dose.

Moderna went with a larger dose — 25 micrograms, or one-quarter of Moderna’s adult dose (which, at 100 micrograms, was larger than Pfizer’s adult dose).

The trade-off is that Pfizer’s vaccine is a three-dose series, spaced out over about 11 weeks. Moderna’s is currently a two-dose series, with the shots spaced four weeks apart. Moderna, though, is testing a third shot for young kids, so it’s possible it may also become a three-dose series.

Do they work?

Both showed sufficient efficacy to be approved, but this answer depends a bit on your expectations.

After three doses, Pfizer showed 80.3% efficacy in preventing symptomatic illness, according to data reviewed by the CDC. Moderna showed 41.5% efficacy.

BUT regulators noted that they have more confidence in Moderna’s number than in Pfizer’s because Moderna’s clinical trial saw more COVID cases among the study participants. In other words, because more kids caught COVID in Moderna’s study (which was larger than Pfizer’s) there was more data to work with to estimate efficacy accurately. Pfizer’s number comes with a much bigger range of uncertainty.

This gets to an issue in trying to compare numbers between the two vaccines: The Pfizer and Moderna studies were conducted differently.

“It’s really challenging to compare the two,” Saporta-Keating said.

Both vaccines showed results that are in line with the vaccines’ efficacy against the omicron variant in adults. They also both produce an immune response in young kids comparable to what the adult vaccines do.

Lastly, de Leon said the main benefit is in preventing severe illness, hospitalization and death, which both vaccines appear to be good at.

“That’s what we’re trying to avoid and that’s what the vaccines are really going to help us do,” he said.

Does one have worse side effects?

The types of side effects reported are similar for the two vaccines, but comparisons are again complicated by the differences in the studies.

For the Pfizer vaccine, the most common side effect in kids ages 2 through 4 was fatigue, which about a quarter of the study participants reported. About 5% of kids in this age range developed a fever. (These numbers are for after the second dose of the Pfizer vaccine, but they are similar for other doses.)

Measuring side effects in younger kids is harder because they can’t always tell you what they’re feeling. But parents of study participants aged 6 months to 2 years reported irritability as the No. 1 side effect, with nearly half experiencing it.

For the Moderna vaccine, fatigue and irritability were also the top side effects. But Moderna generally reported greater prevalence of side effects than Pfizer did. For instance, it reported nearly a quarter of kids in its study ages 2 through 5 developed a fever after the second dose.

De Leon said that may be evidence that Moderna’s larger dose produces larger side effects. But he cautioned parents not to read too much into it, since the studies may define the criteria for side effects differently.

What are the most worrisome side effects?

One child was hospitalized during Pfizer’s clinical trials due to a fever and pain in an extremity that was possibly related to the vaccine. No kids were hospitalized in the Moderna trial, but one did have a fever-related seizure that was possibly connected to the vaccine.

There were no deaths among study participants, and there were no cases of myocarditis — the rare heart condition that has been seen in some older kids following COVID vaccination. There also weren’t any severe allergic reactions.

The studies weren’t necessarily large enough to pick up on all the potential rare side effects, but Saporta-Keating said she wouldn’t expect any hidden problems to be lurking for younger kids that haven’t already been seen in other age groups.

“We have really great now two years of information from the older age groups,” she said.

Does my child need a vaccine if they’ve already had COVID?

Yes, say both doctors.

While previous infection does provide immunity, it’s not clear how long that immunity lasts in children, de Leon said. That makes getting vaccinated important to keep kids protected.

And while it is often thought that young kids don’t suffer from severe COVID, the omicron surge flipped that assumption. According to data presented to the CDC, kids in the 6 months to 5 years age range had higher rates of being admitted to the intensive care unit, being placed on oxygen and being placed on ventilators during omicron than did kids in age groups eligible for vaccination.

This graphic is taken from a presentation given on June 17, 2022, to the Center for Disease Control and Prevention’s Advisory Committee on Immunization Practices. It shows the heavier impact the omicron COVID wave had on children who were at the time too young to be vaccinated. (Screenshot by John Ingold, The Colorado Sun)

Vaccinating a kid who has already had COVID will provide even stronger protection, de Leon said. And he encouraged parents to begin planning for the return to school in fall, when COVID cases have typically surged. Kids need to get their first Pfizer shot now in order to get their third and final dose by early September.

Which one should my child get?

Whichever one you can, Saporta-Keating said.

“My thought process is the one that is available to you is the best one,” she said.

De Leon agreed but added that parents may prefer one over the other based on personal experience and needs. Families in need of a faster timeline or wanting to limit the number of shots will probably prefer Moderna. Families where an older child had strong side effects from a Moderna vaccination may lean toward Pfizer.

Both doctors encouraged parents to talk with their own pediatricians about any concerns, especially if their kids are potentially allergic to any of the components of either or both vaccines.

Elizabeth Morales, 7, receives a COVID-19 booster shot from Andrene Watson on March 13, 2022, at St. Pius X Parish in Aurora. (Olivia Sun, The Colorado Sun via Report for America)

Where can I get a vaccine?

The state is ramping up its distribution system. Colorado has been allocated 31,600 doses in the first two waves of deliveries, and 269 vaccine providers have already signed up to administer them.

Children’s Hospital Colorado is working with the Colorado Department of Public Health and Environment on a series of mobile vaccine clinics. Sign up information is available on the hospital’s website. Kaiser Permanente will be making appointments available on its website. And CDPHE is also keeping a list of available clinics.

How much demand will there be?

Probably a lot, at first.

De Leon said his email inbox was flooded Tuesday with parents seeking information about vaccination.

“This is the one group that’s been missing, so I think there’s a huge appetite to finally make it available,” he said. “This is the one group that’s been left out, and the reason was we had to get it right.”

But how long that demand will last is unclear. Nationally, a Kaiser Family Foundation poll in April showed that only about 1 in 5 parents plan to vaccinate their young child as soon as possible — a much lower percentage than when the question was posed regarding older kids. The number of parents who say they won’t vaccinate their young kids is about the same as with older kids, though.

That puts a plurality of parents in the wait-and-see camp. And it’s why doctors say it’s important for parents to talk with their child’s pediatrician to answer any questions they have.

“This is an exciting time for us,” Saporta-Keating said. “We have the opportunity to get this youngest age group vaccinated and protected against severe disease.”

John Ingold is a co-founder of The Colorado Sun and a reporter currently specializing in health care coverage. Born and raised in Colorado Springs, John spent 18 years working at The Denver Post. Prior to that, he held internships at the Rocky Ford Daily Gazette, the Colorado Springs...