The Bath and West Community NHS Trust this week began a formal inquiry to establish how the mistake was made and to avoid any repetition. The trust says it also wants to establish why the adverse effects which children complained of were not reported back to the trust under established clinical procedure.
Many of the 220 pupils aged 14 and 15 at Devizes school, George Ward school, Melksham, and John of Gaunt school, Trowbridge, suffered swollen arms, high temperatures and flu-like symptoms. They had been given vaccines intended for pre-school children who actually require larger doses than adults or teenagers.
The pupils were given the booster jab following advice from the Department of Health. A resurgence of diptheria in eastern Europe, where more people are now taking holidays, has raised fears.
A letter has been sent to all parents explaining what happened and the inquiry report is expected to be completed in two or three weeks.
Edith Hoffman, deputy head at Devizes school, said that the staff were gravely concerned about the error. "We are obviously as anxious as the parents to know what went wrong. I think it's unbelievable that anything like this can happen," she added.
Kathleen Jones from Devizes said that she was frantic with worry when her son, then aged 15, became violently ill three days after his injection. She called out the doctor at 11pm fearing that he had contracted meningitis.
She said: "I was horrified when I was told what had gone wrong. I couldn't believe they could make such a basic mistake."
The trust said the mistake was only discovered when a doctor at another school noticed the batch of vaccines was too strong.