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Ask Allie: Why are there age brackets for vaccines?

A viewer wanted to know why his 11-year-old can't receive the Pfizer vaccine

ST. LOUIS — Pfizer's COVID-19 vaccine is available for anyone 12 and older and could get approved for younger kids this fall.

But why is the age cut-off 12 years old? That's part of the question from a 5 On Your Side viewer.

The parent said he's concerned about his 11-year-old son who’s not quite old enough to get the vaccine.

Here's the question from Mr V. on Twitter:

"Why is the magic age for shots 12 years old and up? With my son being over 11, and back to in person learning full time in a full-size classroom, it seems it would be safer to vaccinate rather than expose children without the vaccine," he wrote.

Today in St. Louis’ Allie Corey took this question to Washington University infectious disease specialist Dr. Jason Newland as part of our Ask Allie segment.

"First and foremost, we have to make sure things are safe. What we have learned is that if we give an 11-year-old the dose that we are giving the 12- and 13-year-olds, they're going to have a lot more unnecessary side effects. That's why the dose has been changed and that's what we learn with these trials," explained Dr. Newland. "I think we all just need to remember that we have a specific process to do this and we can trust in that process. Creating age brackets helps provide the most safety and understanding the effectiveness in vaccine trials for all age groups."

After Monday's announcement from Pfizer that its vaccine is safe and effective for kids ages 5-11 years old, Dr. Newland estimated we could see it available for that age group under emergency use authorization by November.

New data released by the CDC shows almost half of adolescents are fully vaccinated in the U.S. Right now, 46% of all 12-to-17-year-olds have gotten the shot. That's up from earlier this month. So far, more than 14 million teens have gotten at least one dose.

If you have a question you'd like answered, you can email Allie Corey: acorey@ksdk.com.