Almost 100 schoolchildren were given wrong vaccine jabs during the confusion which followed recent floods in Cumbria, a report has revealed.
Some 93 teenagers at St Aiden's School in Carlisle received an additional whooping cough vaccine, meant for under-fives, in error.
Health officials have blamed a mistake in a telephone order to replace vaccines lost during the floods.
Carlisle and District Primary Care Trust has now amended its procedures.
A report into the 26 January incident was carried out by the trust.
It showed that 93 Year 10 students received the vaccine, which was "slightly different" from the intended one.
They were due to receive two injections - the Diphtheria, Tetanus and Polio vaccine and the Measles, Mumps and Rubella vaccine.
But in addition, they also received vaccination against whooping cough.
The trust investigation found the original and correct batch of vaccines was destroyed during a power failure in Carlisle during the floods which devastated parts of the city over the weekend of 8 January 2005.
An urgent order was placed, but this was done by telephone rather than in writing as is usual.
This resulted in an error in the translation of the order, and Repevax was ordered, instead of the intended vaccine, Revaxis.
Repevax is used for vaccinating children under five and, like Revaxis, contains Diphtheria, Tetanus and Polio but also Whooping Cough.
Dr Rebecca Wagstaff, the city's director of public health, said: "We are all very sorry for the worry this mistake caused for students and their families.
"We have thoroughly investigated how the vaccination error occurred and are already putting the recommendations into place to prevent this happening again. "I would like to say again that the vaccine used had no harmful effects on the students."
As a result of the investigation tighter controls on order checking have been introduced.
Emergency orders will now also be dealt with by fax rather than given over the telephone.