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Side effects of the COVID vaccine in kids under 12

October 28, 2021, 3:30 PM UTC

On Tuesday, the FDA advisory panel backed emergency authorization of a 10-microgram dose of the Pfizer-BioNTech vaccine for children ages 5 to 11, which is equivalent to one-third of the dose given to adults. If the FDA and CDC follow the recommendations of the panel, a vaccine for younger children is expected to be available by the end of next week.

The vaccine has been reported as 91% effective in protecting against symptomatic cases of COVID-19. But similar to adolescents and adults who have already received the vaccine, children in the newly approved age group may also experience some mild side effects after the two doses.

In general, side effects were less common for children ages 5 to 11 than for adolescents and young adults. The side effects were also milder and less frequent for the 2,268 kids in Pfizer’s clinical trial. Pfizer stated that the lower dosage would reduce the frequency of side effects that were seen in older age groups while still providing a strong immune response for children.

According to a briefing document submitted by the company to the FDA, the most common side effect after the second dose was pain at the injection site for around 70% of children. Fatigue and headaches were reported at significantly lower frequencies than by adolescents and adults: 39% of young children experienced fatigue, and 28% reported headaches, compared with 65% and 61% of trial participants ages 16 to 25. Fewer than 10% of children experienced fever, chills, and muscle pain. There were no serious side effects related to the vaccine.

One side effect that did not occur during the clinical trial was myocarditis, inflammation of the heart muscle, an extremely rare but serious side effect. Symptoms often include chest pain, shortness of breath, or an abnormal heartbeat. As Fortune has previously reported, there have been 877 cases of myocarditis out of more than 3.5 million vaccine doses given, according to the Vaccine Adverse Event Reporting System (VAERS). The highest-risk group comprises males ages 16 and 17, but even then the case rate is 0.007%. Nearly all of these vaccine recipients have recovered quickly without any lingering concerns. Pfizer researchers recorded no cases of myocarditis among 5- to 11-year-olds, which was to be expected given the study’s small size and the rarity of the condition, but that age group also generally sees lower instances of myocarditis compared with the rest of the population.

Children between the ages of 5 to 11 account for around 40% of all pediatric COVID-19 cases, one of the highest case rates of all age groups. COVID-19 infection also places children at risk of developing long-term complications like multisystem inflammatory syndrome, which can lead to life-threatening problems in the heart and other bodily organs. Since the beginning of the pandemic more than 8,300 children ages 5 to 11 have been hospitalized for COVID-19, the majority of whom had an underlying condition such as asthma.

“When the virus first came into this country, children accounted for a little less than 3% of cases. Now they account for 27%,” Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, previously told Fortune. “In part because this is much more transmissible, and in part because they are a susceptible group.”

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