More than 1,600 children aged 5 to 11 experienced a systemic reaction such as fever or diarrhea after receiving one of the new COVID-19 vaccines, according to a study from the Centers for Disease Control and Prevention (CDC).

Of 3,259 children in the age group who received an updated Pfizer or Moderna vaccine and were registered in the v-safe system, nearly half experienced a systemic reaction, CDC researchers found.

Systemic reactions, defined as “usually mild” and lasting for multiple days, include fatigue, chills, nausea, abdominal pain, vomiting, joint pain and diarrhea. On a severity scale, the category of reactions is between local reactions and severe reactions.