The most common COVID vaccine side effects for babies and toddlers under 5

• Pfizer and Moderna both have COVID vaccines for children as young as 6 months old — which may begin going in arms next week.
• Both companies say side effects for babies and toddlers are generally milder than for older people.

The wait is almost over for US parents who've been anxiously awaiting the authorization of a COVID-19 vaccine for babies and toddlers under 5 years old.

Independent advisors to the Food and Drug Administration voted unanimously on Wednesday, encouraging the regulatory agency to give the green light to COVID-19 vaccines from Pfizer and Moderna for kids as young as 6 months old. (The move still requires a final go-ahead from the FDA and from the Centers for Disease Control and Prevention this weekend, meaning shots may finally start going in kids' arms next week.)

Ahead of the FDA's public meeting, the agency released independent analyses of both pediatric vaccines. The analyses suggest the shots from both drug makers are safe and effective at curbing COVID-19 — though like the shots for adults, they don't prevent coronavirus infections entirely, especially with the highly-infectious Omicron variant circulating.

The FDA reviews of Pfizer and Moderna baby vaccines include breakdowns of the most common side effects for each brand, broken down by age.

Moderna's vaccine, which includes a higher dose of mRNA than Pfizer's, comes with more side effects, while Pfizer's low-dose vaccine takes longer to kick in. But both vaccine formulations for babies and toddlers are much milder than the adult versions, and come with tamer side effects overall as a result.

Side effects from these COVID-19 vaccines, if they surface, usually begin about a day or two after vaccine administration and last for about 24-48 hours, on average. Though they're a bit unpleasant, they're also a sign that the vaccine is working, and the body's immune system is revving into gear. However, many babies and toddlers never experience much of a reaction to their COVID-19 vaccine at all, and that is also perfectly normal.

The most common side effect for babies who recieved Pfizer's 3-shot vaccine was irritability

In Pfizer's 6 month to 2 year age group, the top side effects were:

1. Irritability (51%)
2. Drowsiness (27%)
3. Decreased appetite (22%)
4. Tenderness at the injection site (17%)
5. Fever (7%)

Babies who got Moderna's 2-shot vaccine were also irritable for a couple days afterwards

In Moderna's 6 month to 2 year age group, the top side effects were:

1. Irritability (82%)
2. Pain at the injection site (56%)
3. Drowsiness (51%)
4. Decreased appetite (46%)
5. Fever (22%)
6. Swelling and redness at the injection site (18%)

Toddlers who got Pfizer's vaccine were tired, and had some arm pain

Toddlers who got Pfizer's vaccine had relatively few side effects.

Study participants from 2 to 5 years old reported:

1. Pain at the injection site (31%)
2. Fatigue (30%)
3. Injection site redness (11%)

Most toddlers who got Moderna had some arm pain

2 year olds who got Moderna's vaccine had similar symptoms to the babies in the study, including:

1. Pain at the injection site (77%)
2. Irritability (71%)
3. Drowsiness (50%)
4. Decreased appetite (42%)
5. Fever (26%)
6. Injection site redness (18%), swelling (16%)

Symptoms for 3 to 6 year olds who got Moderna were more similar to those that older kids and adults experience

Kids from 3 to 6 years old who got Moderna's two shot vaccine experienced:

1. Pain at the injection site (84%)
2. Fatigue (62%)
3. Headache (23%)
4. Muscle aches (22%)
5. Fever (21%)
6. Chills (17%)
7. Nausea, vomiting (15%)
8. Swelling, tenderness (14%)

It's too early to know what the true vaccine effectiveness of these shots is

Both Moderna and Pfizer released some early estimates of their vaccine effectiveness for kids (based on trials in a few thousand volunteers) but it's worth treating both numbers with a healthy dose of skepticism, given their highly preliminary nature.

Pfizer's estimated its vaccine was around 80% effective, a number that was based on only 10 COVID-19 cases observed over the course of 40 days. Moderna's roughly 40% to 50% vaccine efficacy estimate for kids 6 months to 6 years old doesn't include a third dose (booster), which the company is testing out in that age group now.

Dr. Amanda Cohn from the CDC said during the meeting on Wednesday that "I would really hope" people don't put too much stock in the differing effectiveness numbers, because they are based on such a small number of cases over a very short period of time.

"I believe the vaccine is effective, I do not have any idea what that number will actually end up being," she said.

The true measure of success for these vaccines will be seen over time, based on how well they do at keeping young kids out of the hospital, and at preventing more COVID-19 deaths among babies and toddlers. COVID-19 hospitalization and death rates have been higher in kids under 5 than among school-aged kids (from 6-17 years old) who have already had the option to get vaccinated against the virus for many months.

"I think we have to be careful that we don't become numb to the number of pediatric deaths because of the overwhelming number of older deaths," Dr. Peter Marks, who's in charge of the FDA's vaccine-regulating Center for Biologics Evaluation and Research, said at the meeting, stressing that the hospitalization rate in young kids has been "troubling" and the pediatric death trends are far worse than even a very bad flu year.

"Every life is important. Vaccine-preventable deaths are ones that we would like to try to do something about," he said.