Effects in six of the children after a first dose included a mild rash, headache, diarrhoea, presumed sore throat, neck pain, difficulty sleeping, and low blood sugars.
But all of these had gone away within 72 hours, according to the study, which is due to be published in the Archives of Disease in Childhood.
Five of the children had effects including diarrhoea, vomiting, armpit swelling, and blisters around the mouth after the second dose.
The researchers said fever was more common than in adult studies, with 13% of the children having a temperature greater than 38C compared with 4% in people aged between 16 and 55.
Other recorded adverse events all resolved within a week, the study by scientists from the department of paediatric immunology and infectious diseases at Bristol Royal Hospital for Children and the University of Bristol noted.
They said: “Numbers were small but these data are especially important as they are representative of the children who are most likely to benefit from vaccination and parents and clinicians may have concerns regarding an increased risk of unexpected events.”
Reassurance for Parents
Russell Viner, professor of adolescent health at UCL Institute of Child Health, noted that the study “should reassure parents and doctors that there are no special precautions or issues with this vaccine in this small group of children”.
He added: “However these data can tell us very little about rare side effects or about vaccinating healthy teenagers or those with common conditions such as asthma and diabetes. For that we must await further data in the order of millions of doses.”
Dr David Elliman, a consultant paediatrician at Great Ormond Street Hospital, said: “This is a small study, as the authors point out, and it is not explained how these patients were chosen to be included.
“It is useful to know the nature of the reactions to the vaccine, not all of which were minor, but because of the size of the study it would be unwise to assume that this picture could be generalised to a larger group of similar children.”