Pfizer COVID Vaccine for Younger Children Hits Snag


Dec. 17, 2021 — Pfizer’s COVID-19 vaccine for children ages 2 to 5 years old fizzled in clinical trials, the company said on Friday, signaling a further delay in getting a vaccine to preschoolers just as Omicron bears down on the U.S.

In a news release, Pfizer reported that while its 3-microgram dose — which is less than one-third of the dose given to older children — generated a protective immune response in babies and toddlers ages 6 to 24 months, it didn’t generate adequate immunity in children ages 2 to 5.

The company plans to change its clinical trial to add a third dose for younger children in hopes of improving those results. It also plans to test a third dose of its 10-microgram vaccine for children ages 5 to 12.

If the trials are successful, Pfizer said it would submit data to the FDA for an emergency use authorization (EUA) in the first half of 2022.

That pushes the timeline of getting a vaccine to younger children back by several months. In November, Anthony Fauci, MD, head of the National Institute of Allergy Infectious Diseases, predicted a vaccine would be ready for preschoolers by spring.

“On one hand, parents are understandably disappointed,” said Jill Foster, MD, a pediatric infectious disease doctor at the University of Minnesota Medical School. “On the other, it shows that the system for testing vaccines is working. Children are not little adults and have complex immune systems, so it’s not just a matter of making the dose smaller and expecting that it will work,” she said, noting that data from Moderna’s KidCOVE study in preschoolers is pending.

How Do COVID-19 mRNA Vaccines Work?Some of the COVID-19 vaccines are known as mRNA shots. How are they different from traditional vaccines? And do they contain the real virus?189


SPEAKER: How does a COVID-19

mRNA vaccine work?

COVID vaccines are now


Some of the COVID-19 vaccines

are mRNA vaccines, but what does

this mean?

mRNA vaccines are

different from traditional


mRNA vaccines don't expose you

to any real virus instead,

they're made with messenger

Ribonucleic Acid or mRNA.

This is a type of molecule that

gives instructions to the cell

for how to make different kinds

of proteins.

mRNA molecules are

a natural part of our cells

and how our bodies work.

Researchers have been working

with mRNA vaccines

for many years.

They are made more easily

and safely in a lab

than a vaccine that uses

a virus.

Because of this they can also

be made faster.

The COVID-19 mRNA vaccines

have passed many tests in labs

and in thousands of people,

and meet strict standards

from the FDA.

So how do these vaccines work?

First, a COVID-19 mRNA vaccine

is injected into a muscle

in your upper arm.

Some muscle cells take the mRNA

instructions in the vaccine

and make a harmless piece

of a protein called

a spike protein.

This protein is found

on the outside of the SARS-CoV-2

virus that causes COVID-19.

The muscle cells then destroy

the instructions for how to make

the spike protein.

The mRNA never goes

into the nucleus of your cells

where your DNA is stored.

The newly made spike protein now

sits on the surface

of the muscle cells.

Your immune system senses

the spike protein

as a foreign threat to destroy,

it starts making antibodies

to fight anything

with that spike protein on it.

This will help your body's

immune system recognize

and fight the real virus if it

ever shows up.

It's like recognizing someone

by the hat they wear.

Your body is then

prepared to spot COVID-19

and fight it off before it grows

in your body's cells.

Fast facts to remember

about COVID-19 mRNA vaccines.

They help get your body

ready to fight off the COVID-19

virus before it makes you sick,

they don't use

any live, dead, or weak virus,

they can't give you COVID-19,

they don't affect your DNA.

Want to learn more,

go to to find more

information about mRNA vaccines.

You can also learn more about

how the vaccines were approved




From Krames/delivery/aws/e1/19/e1194689-aff0-4d9e-9fd2-2c0084642589/b37084c0-2e1f-4b66-958c-96e7a6c3f4db_krames_activating_health_how_mrna_vaccine_works_021021_,4500k,2500k,1000k,750k,400k,.mp402/10/2021 12:00:0018001200photo of COVID-19 mRNA vaccine/webmd/consumer_assets/site_images/article_thumbnails/video/1800x1200_krames_activating_health_how_mrna_vaccine_works_video.jpg091e9c5e8210a400

Until there’s a vaccine, Foster says parents should protect babies and toddlers by making sure everyone around them is vaccinated, promote the use of face masks for everyone around them and for all children over age 2, and continue to avoid crowded gatherings, particularly those that are indoors.

“Hand sanitizer is important, but this virus, especially the Omicron variant, is very easily spread through the air, so keep the air clear of virus as much as possible,” she said.

While the youngest children are still waiting for an effective vaccine, there was reassuring news Thursday about the safety of Pfizer’s vaccine for school-aged kids — those ages 5 through 11.

Out of more than 7 million doses given since this vaccine was authorized for emergency use in late October, most reactions to the vaccine — including arm pain, swelling, and fatigue — have been mild and gone away quickly, without the need to miss school or see a doctor, the CDC reported to a meeting of its Advisory Committee on Immunization Practices, or ACIP, on Thursday.

Many experts had been waiting to see if this vaccine would cause rare cases of heart inflammation called myocarditis, as a higher dose did in teens and young adults.

The news on this front was excellent. About 6 weeks after this vaccine became available, the CDC says there have been only eight confirmed cases of myocarditis in this age group. Six more cases are under investigation.

To put this risk into context, data collected by the American Academy of Pediatrics and the Children’s Hospital Association shows that about 1% of children who test positive for COVID-19 are hospitalized for their infections, while the risk of getting a case of myocarditis after vaccination is .0002%, making it about 5,000 times more likely that a child would need to be hospitalized for COVID-19 than for myocarditis after vaccination.

John Su, MD, who is a member of the CDC’s Vaccine Safety Team, reported there had been two deaths in children after a COVID-19 vaccination. Both were girls, ages 5 and 6. Both had complicated medical histories for several medical disorders. It’s not clear their deaths were linked to the vaccine, and the causes of their deaths are still under investigation.

Show Sources

Jill Foster, MD, pediatric infectious disease doctor, University of Minnesota Medical School, Minneapolis.

John Su, MD, Vaccine Safety Team, CDC COVID-19 Vaccine Task Force.

CDC Advisory Committee on Immunization Practices, Dec. 16, 2021.

News release, Pfizer, Dec. 17, 2021.

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