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Nicole Karlis

Why the kids' vaccine took so long

A nurse gives a little girl a shot of the Pfizer COVID-19 vaccine while her brother covers his eyes at a vaccination site for 5-11 year-olds at Eastmonte Park. Paul Hennessy/SOPA Images/LightRocket via Getty Images

At last, parents of kids under the age of five — many of whom felt left behind during the pandemic — can breathe a sigh of relief.

At last, a COVID-19 vaccine for the youngest children is expected to be recommended for emergency use authorization (EUA) in the coming days. The news comes as an FDA advisory panel voted in favor of recommending authorization of the Pfizer and Moderna vaccines for kids under 5 on Wednesday —  the first step in a multi-step process for full authorization.

While the news has been met with relief, many parents have waited over two years to have the option to protect their little ones. Moreover, in that span, there were multiple points at which rumors circulated that vaccines for children under five were going to be approved imminently; again and again, parents found their hope dashed. In May, mass vaccination sites across the country — including in Chicago and Seattle — were allowing parents to book vaccination appointments for their children, though a delay ensued.

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At the end of 2021, health officials in the Biden administration hoped to authorize shots by Pfizer and BioNTech for kids between the ages of six months and five years sometime in early 2022, possibly by February 2022. But when February 2022 rolled around, the possibility of any authorization was pushed to spring; then, the Food and Drug Administration (FDA) stated that the agency wanted more data submitted around the possibility of a three-dose Pfizer vaccine amid concerns of the omicron variant affecting the vaccine's efficacy. (Notably, Moderna's two-dose vaccine appeared to offer more protection against omicron.)

"It has been rough. We have two school aged kids and never knew when or what they were bringing home. It was like playing Russian roulette," Griffen Miller, 36, told Today regarding the recent endorsement. "So, honestly, I thought it was about time. We went so long without protection for that age group. It didn't make sense."

"The bar is set really high for the safety issue ... We know that the vaccines don't protect as well against omicron, so it's kind of a moving target in terms of the effectiveness that you're aiming for."

So, why did it take so long to get to where we are today? Countries like China, Argentina, Venezuela, Croatia, Germany, Greece, Hungary and Spain have already offered vaccinations for kids under five. The answer has to do with emerging variants; the difficulties of running clinical trials on children; and unsatisfactory results from clinical trials around how much protection the vaccines provide. To be clear, safety and side effects were never a reason for a delay.

"The bar is set really high for the safety issue, [but] it's difficult to do the effectiveness studies,"  Dean Blumberg, associate professor of pediatrics at the University of California–Davis, previously told Salon. "We know that the vaccines don't protect as well against omicron, so it's kind of a moving target in terms of the effectiveness that you're aiming for."

One of the principal challenges in vaccine design stems from the fact that children have a different immune system than adults, which makes weighing dosage adjustments and immunity a complicated balancing act. This always made it more difficult for clinical trials to occur for this cohort.

"Children have different, less experienced immune systems, and they also are different sizes compared to adults," Blumberg said. Essentially, younger children's immune systems are "less mature," Blumberg added, and they typically have less body mass than adults. Generally, this means an adjustment in vaccine dosage — either more or less than adults to create a healthy and protective immune response. As a result, Pfizer' shot for kids is one tenth of the dosage for adults, and Moderna's is a quarter of what's administered to adults.

Moreover, since clinical trials were conducted when the omicron variant began to spread, protection with Pfizer's two-dose vaccine was lower for kids, which affected the calculus of the dosage. Hence, the need for a three-dose vaccine, which is what is expected to be approved now.

According to the most recent data from Pfizer, its three dose vaccine provides 75 percent efficacy against COVID-19 in kids between six months and two-years-old, and is 82 percent effective against omicron in two to four-year-olds.

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However, during the FDA's Wednesday meeting, concerns were raised about the logistics of getting three doses in kids' arms, as the third dose is key to providing real protection. With only two doses, the vaccine is a mere 14 percent effective for kids under age 2, and 33 percent effective for those ages 2 to 4, specifically tested on omicron. Notably, while Pfizer's second dose is given three weeks after the first; the third is given at least eight weeks after the second.

"I do worry that parents aren't necessarily going to know that after two doses, they may not be protected at all and will engage the kind of activity that would put their child at risk," Dr. Paul Offit, an FDA committee member, an FDA committee member, said.

Ultimately, the committee agreed that the benefits outweigh the risk.

Moderna's two-dose vaccine is estimated to be about 51 percent effective against omicron for six-month-old to 2-years-old, and about 37 percent effective for children ages 2 to 5-years-old.

While Wednesday's meeting was a promising step forward, nothing is for certain yet. Next, an expert panel that advises the Centers for Disease Control and Prevention will convene to make their recommendation. As soon as that happens, a final recommendation could be made by the FDA which will likely lead to CDC Director Rochelle Walensky formally signing off on the recommendations in the next week. This could mean that kids between the ages of six months old and five could start getting vaccinated as early as next week.

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