The Pfizer COVID vaccine for children ages 5 to 11 has been shown to be as safe as expected so far, with just 100 “serious” events reported in the 8.7 million first doses, the CDC said Thursday.

The government cleared the vaccine for children in this age group in early November, making about 28 million people eligible for the vaccine. However, participation has been slow so far, and there is now pressure to immunize young children – especially with the sharp increase in late pediatric hospitalizations.

Against this background, the CDC released a review of the vaccine’s safety profile from November 3 to December 19, during which time the Vaccine Adverse Event Reporting System (VAERS) received 4,249 reports. Of these, all but 100 were classified as “non-serious reports”, such as vomiting, headache, or rash.

Of the 100 “serious” reports, most were for fever and vomiting. There were 10 reports of seizures (three of which had a previous history of seizures) and 9 reports of intensive care hospital admissions.

During the investigation period two children died – girls aged 5 and 6 who had other underlying conditions and were already in “fragile health” before the injections. The CDC said there was no data to link their deaths to the gunfire.

Separately, the agency also released data from the voluntary “v-safe” telephone registration system, based on complaints reported within a week of receiving each dose of vaccine.

Of 42,000 children enrolled after their first dose, about 35% had some sort of “systemic reaction”, most often fatigue or headaches. For the nearly 30,000 of those same children with second dose data, 41% had similar systemic reactions. About 11% missed at least one day of school after their second dose.

“Parents and guardians of children aged 5 to 11 should be informed that local and systemic reactions are expected after vaccination with the Pfizer-BioNTech COVID-19 vaccine and are more common after the second dose,” said the CDC in its report.