At long last, kids are starting to filter into pharmacies and clinics for COVID-19 shots.

The Food and Drug Administration authorized a lower dose of Pfizer’s vaccine for emergency use in children ages 5 to 11 in October. Then last week, the Centers for Disease Control and Prevention officially greenlit the shot for this younger age group – nearly a year after the first Americans started receiving COVID-19 vaccines.

Kids receive one-third of the standard dose of the mRNA shot given to adults: 10 micrograms versus 30 micrograms. Because of that, children can generally expect fewer side effects.

The chart below shows the most common side effects among kids ages 5 to 11 in Pfizer’s clinical trial.

Fatigue was by far the most prevalent side effect: More than one-third of kids reported it after the first or second dose. Roughly one-quarter of kids also reported headaches after getting either dose.

Overall, kids reported more side effects – including muscle pain, chills, and fever – after dose two than dose one. That’s likely because the second shot amplifies an existing immune response. However, an uncommon side effect, vomiting, had the same rate of occurrence (2%) after the first dose as it did after the second.

Kids had more redness and swelling at the injection site, but adults had more headaches and fatigue

Kids’ milder side effects were similar to those reported among older people (ages 56 and up) in Pfizer’s clinical trials. Adolescents and younger adults, on the other hand, typically experience more intense and frequent side effects after their shots.

There’s one notable exception, though: Kids ages 5 to 11 had more redness and swelling at the injection site than adolescents or adults. Children also reported more pain at the injection site after the first dose (74%) than after the second (71%).

Among adults, nearly half of people ages 18 to 55 reported fatigue after their first Pfizer dose, and around 60% reported fatigue after their second. Headaches were also common: 42% of adults in that same age group reported a headache after the first dose, and 52% after the second.

The chart below shows how side effects differ based on age group, vaccine manufacturer, and dose received. Data comes from clinical trials.

Mild or moderate aches and pains after a vaccine are normal, since vaccines prompt our bodies to produce coronavirus antibodies. Our immune systems don’t distinguish between a real infection and a vaccine-induced response, so they still release inflammatory chemicals to protect us. That’s why people often develop fever, muscle pain, fatigue, or headaches shortly after getting vaccinated.

It’s a small price to pay for protection against severe COVID-19: Two doses of Pfizer’s vaccine lower the risk of hospitalization by roughly 90% for adults, according to a study published last month in The Lancet. And two 10-microgram doses were 91% effective at reducing the risk of symptomatic illness in 5- to 11-year-olds in clinical trials.

Though COVID-19 tends to be milder in kids, more than 170 children ages 5 to 11 have died from the disease in the US, making it a leading cause of death for that group. The CDC estimates that every 1 million COVID-19 vaccines administered to young kids could prevent hundreds of children from being hospitalized.