The Pfizer COVID Vaccine for Kids: How Does It Differ?

Sandra Adamson Fryhofer, MD


November 12, 2021

This transcript has been edited for clarity.

A two-dose "kiddie" vaccine is now available for the 28 million children aged 5 through 11.

Why Kids Need COVID-19 Vaccination

COVID-10 can be a killer for young kids. If you look at the top 10 causes of death for children in this age group over the past year, COVID-19 comes in number eight. Children aged 5 through 11 years make up 40% of all pediatric COVID cases. In this age group alone, there have been more than 1.9 million COVID-19 cases, over 8300 hospitalizations due to COVID-19, and 94 deaths since the pandemic began.

COVID-19 has hit minority children especially hard. Multisystem inflammatory syndrome in children (MIS-C) is most frequent among kids aged 5 through 11 and has affected at least 2316 children in this age group so far. Two thirds of MIS-C cases occur in Black and Hispanic children.

Hospitalization rates show disparities, too. Compared with White children, hospitalization rates are three times higher for children who are Black, Hispanic, or American Indian/Alaska Native.

Overall, hospitalization rates for COVID-19 in kids are similar to those for flu — but for COVID-19, the hospital stays are longer. One third of those hospitalized with COVID-19 required intensive care unit (ICU) admission. More than two thirds (68%) of those hospitalized had at least one underlying medical condition predisposing them to severe COVID, such as asthma or obesity. One third of those hospitalized did not have a predisposing medical condition but got severe COVID anyway.

Post-COVID conditions can also occur in children. Kids can be long haulers, too! Post–COVID-19 conditions do not just occur after severe cases. Children can have persistent fatigue, headache, sleep problems, trouble concentrating, muscle and joint pain, and cough, even after mild COVID-19 infections.

COVID-19 has greatly affected quality of life for children in this age group. COVID-19 mitigation and precautions have placed limitations on physical activity and social interactions. Many children have lost in-person learning owing to school closures and missed school owing to quarantine after exposure or illness.

Children in this age group are at least as likely as adults to be infected with COVID. However, infections in children are less likely to be reported than cases in adults. Secondary transmission from children occurs at both at school and at home.

How Pfizer's Pediatric Vaccine Differs From the Adult Vaccine

Different dose size, same time interval. The kiddie dose for those 5 through 11 is 10 µg. This is one third of the dose given to adults and older children (aged ≥ 12 years). The 3-week interval between doses in the two-dose series remains unchanged and mirrors the time interval for adults.

Different buffer. The mRNA and its nanoparticle coating are the same for both versions. The buffer used to stabilize them is different. The kiddie dose buffer is tromethamine (Tris). The adult version buffer is phosphate-buffered saline (PBS). This new Tris buffer formulation makes the children's version of the vaccine more stable, so it can be stored for longer at regular refrigerator temperatures. The vials of the children's version can be stored unopened and undiluted in regular refrigerators for up to 10 weeks.

Different color code. To avoid confusion, the two age-based products are color-coded to make them look different. The adult version vial top and packaging are purple. The vial top and packaging for the kids' version are orange.

Vaccine effectiveness. Vaccine authorization was based on immunobridging and compared neutralizing antibody titers after two kiddie doses in 5- through 11-year-old children with titers from 16- through 25-year-old teens and young adults who received two adult-size doses. Vaccine efficacy for a two 10-µg dose series in 5- through 11-year-old children is 90.7%.

Vaccine side effects. Side effects include pain, redness, and swelling at the injection site, as well as fatigue, headache, and chills. Children aged 5 through 11 (who received the 10-µg dose) had less fever than the 16- through 25-year-old teens and young adults who received a 30-µg dose.

Myocarditis risk after mRNA vaccines. There were no reports of myocarditis in the more than 3000 children who received the Pfizer kiddie dose vaccine, although the study was small. Rates of postvaccination myocarditis previously reported are based on data from adults and adolescents receiving the larger adult 30-µg dose and not the smaller pediatric 10-µg dose. Myocarditis can occur after COVID-19 infection. On the basis of studies of adults, older adolescents, and teens, the risk is higher after COVID-19 infection than after mRNA vaccination. The rate of myocarditis after mRNA vaccination in children aged 5-11 years is still unknown. CDC safety surveillance for postvaccination myocarditis will continue.

Is It Safe for Kids to Get Vaccinated if They Have Already Had COVID-19?

In the clinical trials, 9% of children were previously infected with COVID-19. These baseline seropositive children had milder side effects after vaccination compared with those who were never infected. Postvaccination antibody levels in baseline seropositive children were higher than titers in children who had never had COVID.

The Delta wave surge of pediatric hospitalizations for COVID occurred even though 38% in this age group were already seropositive. This suggests that past infection alone is not sufficient to provide broad protection against COVID.

When to Vaccinate Children 'on the Bubble' (About to Turn 12)

For children who are about to turn 12, parents have to decide whether to vaccinate now (at age 11) with the lower 10-µg dose or wait until the child qualifies for the higher 30-µg dose vaccine.

At a meeting of the Vaccines and Related Biological Products Advisory Committee (VBRPAC), the FDA's independent advisory committee, Pfizer representatives were asked this question. They responded with data showing that neutralizing titers in 5- through 11-year-old children who received a 10-µg dose were just about the same as titers in 16- through 25-year-olds who received a full 30-µg dose. These data would suggest that we should go ahead and vaccinate as soon as possible.

How convenient that a COVID-19 vaccine is available for kids aged 5 through 11 just in time for this year's holiday season. About half of parents surveyed already say they are likely to get their child vaccinated. When asked about a preferred location for child vaccination, their regular physician's office was by far the favorite first choice.

COVID-19 is now vaccine-preventable. I encourage parents of children aged 5 through 11 years to protect them from COVID-19 by getting them vaccinated with this children's dose formulation of Pfizer-BioNTech's mRNA COVID vaccine.

For Medicine Matters, I'm Dr Sandra Fryhofer

Follow Medscape on Facebook, Twitter, Instagram, and YouTube


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.