Will kids get the same Pfizer COVID vaccine dose as adults? Here’s what to know

·5 min read

Now that children between 12 and 15 years old can safely receive the two-dose Pfizer-BioNTech coronavirus vaccine, some parents and curious kids alike may be wondering how the shot for teens differs from those given to adults.

The short answer is not at all.

For starters, the dose size is the same. Like adults, kids will be given the same amount of vaccine in two doses, three weeks apart, according to the U.S. Food and Drug Administration.

That’s usually the case with most vaccines, apart from some exceptions. For example, adults are given higher doses of the Hepatitis B vaccine than children, whereas kids are given higher doses of the Tdap (Tetanus, Diphtheria, Pertussis) shot than adults.

“However, once we get younger than [12 years old], we have to slow things down a little bit and make sure we have the right dose that is safe and effective for younger children,” Dr. Michael Smith, a Duke University pediatrician and infectious disease specialist involved in the pediatric trials of the Pfizer vaccine, said during a Tuesday media briefing.

Ongoing clinical trials are testing both the Pfizer and Moderna coronavirus vaccines in children as young as 6 months old.

‘It’s pretty much one size fits all’

Vaccines aren’t like medications in that older, heavier or taller people may need more of it to benefit from its effects.

“Vaccines work differently because it’s not about having a certain level of it in your blood, it’s about stimulating the immune system, and most people’s immune system’s will react to a very small amount of whatever it is that they’re being exposed to,” Dr. Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security, told McClatchy News in January.

“So, it’s not a dose-response relationship. It’s about finding the perfect dose for the immune system to get the right amount of stimulation, and for most vaccines, it’s pretty much ‘one size fits all,’” Adalja added.

Put another way, the vaccine itself doesn’t travel through your body. It’s your cells that pick up directions from the shot and deliver them throughout your immune system, similar to a retail warehouse (vaccine) and its delivery drivers (cells).

So, no matter how large or small someone is, the amount of vaccine doesn’t make a difference; the lowest dose that offers the best protection and proves to be safe is the one that becomes the standard for any vaccine. That’s why experts don’t recommend delaying or avoiding vaccination of any type for kids who are either overweight or underweight.

Just think about how tiny viruses and bacteria are. The coronavirus is 60 to 140 nanometers across. For reference, a sheet of paper is about 100,000 nanometers thick. All it takes is a microscopic amount of virus to make someone sick. “That type of principle really applies to vaccines,” too, Adalja said.

“Because immune systems have evolved to respond to such minute quantities of something they deem foreign, for most vaccines it’s the same dose no matter what your size is,” he said.

This also means a person’s size doesn’t affect how quickly they are able to gain immunity from a COVID-19 vaccine, Adalja added.

Although the Pfizer vaccine has been authorized for kids ages 12-15, children won’t be able to get vaccinated until the Centers for Disease Control and Prevention meets on Wednesday to discuss how to best distribute the shots among the age group.

With that being said, “it’s quite possible that children can receive this vaccine as early as Thursday,” Smith noted, assuming the CDC’s director signs off on the vaccination plans right away.

How well does the Pfizer COVID-19 vaccine protect children?

Pfizer announced in March that its vaccine reduced risk of coronavirus infection in children 12-15 years old by 100%, meaning no vaccinated kids were infected during the late stage trial.

It’s a stunning boost in protection against COVID-19 compared to people between 16 and 25 who benefit from a 95% reduction in infection risks after receiving their final of two doses.

But 100% efficacy during clinical trials doesn’t guarantee that the same level of protection will be seen in the general population, which includes millions of kids, not thousands.

“Just as we saw in the adult population, even if the vaccine does not prevent [kids] from getting COVID, it’s very, very effective at reducing severe disease and reducing hospitalization,” Smith said. “So, I have no doubt in my mind that this is a good idea, if you have a 12- to 15-year-old at home, to give them the vaccine.”

Side effects in children such as arm pain, fatigue, headache and joint pain were comparable to those in adults. No serious allergic reactions were reported among the kids in the study.

The trial included 2,260 children between 12 and 15 years old in the U.S. with or without histories of past coronavirus infections. Among the kids who received a placebo shot, 18 developed COVID-19, while none who got the vaccine developed the disease.

The company did not mention how well its vaccine worked against the more contagious coronavirus variants, but the variants have been spreading during the late stage trial period.

Side effects were similar to those experienced in adults and included injection site pain (84%), fatigue (63%), headache (55%), muscle pain (38%), chills (32%), joint pain (24%), fever (14%), injection site swelling (10.5%) and nausea (1%).

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