Safety of Bivalent mRNA COVID-19 Boosters in Children Aged 5–11 Years

Early safety data published in January 2023, covering October 12, 2022 to January 1, 2023. COVID-19 vaccine recommendations may have changed since; see CDC's current guidance.

In brief. After CDC recommended bivalent COVID-19 boosters for children aged 5–11 in October 2022, children in that age group received about 953,359 bivalent booster doses by January 1, 2023. Early reports to v-safe and the Vaccine Adverse Event Reporting System (VAERS) looked like those after the original (monovalent) booster. Most VAERS reports were about vaccination errors rather than adverse events, and there were no reports of myocarditis or death. The report's authors said these findings should be shared when counselling parents and guardians.

Background

On October 12, 2022, the Food and Drug Administration (FDA) authorised bivalent Pfizer-BioNTech and Moderna mRNA vaccines — encoding the spike protein of the original virus and of the Omicron BA.4/BA.5 variants — as a single booster at least 2 months after the primary series or a monovalent booster: Pfizer-BioNTech for ages 5–11 and Moderna for 6–17. On December 8 the authorisations were extended to children as young as 6 months. The Advisory Committee on Immunization Practices recommended an age-appropriate bivalent booster for everyone 6 months and older. Safety in people 12 and over had already been described.

From October 12 to January 1, 861,251 children aged 5–11 received the Pfizer-BioNTech bivalent booster and 92,108 aged 6–11 received Moderna's.

Two monitoring systems

• v-safe — a voluntary smartphone-based system set up by CDC. A parent or guardian can register a child under 15 and answer daily health surveys for the week after vaccination about injection-site and whole-body (systemic) reactions and their effects. Call-centre staff follow up on anyone who reports getting medical care.
• VAERS — a passive reporting system run jointly by CDC and FDA. Anyone can report; providers in the CDC COVID-19 Vaccination Program must report adverse events and vaccination errors. Serious reports — hospitalisation, life-threatening illness, permanent disability, birth defect or death — are reviewed by CDC physicians, and possible myocarditis is searched for specifically.

v-safe: 3,259 children

Of the 3,259 registered children aged 5–11 who got a bivalent booster, 2,647 (81.2%) received Pfizer-BioNTech and 612 (18.8%) Moderna. About 20.6% (670) got another vaccine at the same visit — 649 of them a flu shot.

• The most common reactions were injection-site pain (65.9%), fatigue (33.0%) and headache (22.9%). Most were mild — noticeable but not a problem — and were most often reported the day after vaccination, tapering off after.
• On at least one day, 469 children (14.4%) could not go to school and 447 (13.7%) could not do their usual activities.
• 62 parents or guardians (1.9%) sought medical care for their child, most often at an outpatient clinic (37); no child needed hospital care. Where more detail was available, the parents of 35 of 37 children said the visit was unrelated to vaccination.

Reactions and their effects were more common after Moderna than Pfizer-BioNTech, as seen before with mRNA vaccines.

VAERS: 922 reports

VAERS processed 922 reports for children aged 5–11 (median age 9; 49.8% girls). 920 (99.8%) were not serious.

Vaccination errors made up 775 reports (84.2%), for example:

• wrong dose (303) — often a child given the adult dosage;
• wrong product formulation (207);
• vaccine prepared incorrectly (177) — often reconstituted wrongly;
• product given to a child of the wrong age (126) — including a bivalent booster given in place of a monovalent primary-series dose.

Only 74 (9.5%) error reports described any health event.

Of the 145 non-serious reports that were not errors, the most common events were fever (21), fainting (20), vomiting (18), nausea (17) and dizziness (14).

The two serious reports both followed Pfizer-BioNTech: one child had symptoms consistent with Miller Fisher syndrome, a rare acquired nerve disorder considered a variant of Guillain-Barré syndrome (confirmation from medical records was pending), and one was hospitalised with hives and arthritis. No myocarditis and no deaths were reported.

What it means

These first 11 weeks broadly matched surveillance of the monovalent booster in this age group. Reactions were as frequent as after the monovalent Pfizer-BioNTech booster, and most medical visits were unrelated to vaccination. After more than 950,000 doses there were only two serious VAERS reports.

Vaccination errors were a large share of reports in children after both monovalent (71%) and bivalent (84%) boosters, compared with 35% among people 12 and over after the bivalent booster. Most errors caused no health problem, and those that did matched expected mRNA reactions. CDC updates clinical guidance, educational materials and training after each change in recommendations, and public health officials should keep training vaccinators to cut errors in children.

The authors concluded that the early findings were reassuring. Serious health effects after mRNA vaccination are rare, whereas SARS-CoV-2 infection can cause death and serious long-term effects, and bivalent vaccines add significant protection against symptomatic infection. CDC and FDA would keep monitoring safety.

Limitations

• v-safe is voluntary and may not represent all vaccinated children.
• v-safe does not record whether a dose was monovalent or bivalent, so some children who aged into the group without a completed primary series may be misclassified.
• VAERS is passive and subject to reporting bias and under-reporting, especially of non-serious events.
• The 11-week window limits the conclusions; monitoring continues.

The report gives the medical-care count as both 62 and 64, and the share of VAERS reports that were errors as both 84.2% and 85.0%.

Sources

• Hause AM, Marquez P, Zhang B, et al. Safety Monitoring of Bivalent COVID-19 mRNA Vaccine Booster Doses Among Children Aged 5–11 Years — United States, October 12–January 1, 2023. MMWR Morbidity and Mortality Weekly Report, CDC (corrected version).