Fourteen children had to be revaccinated in the past three months after an improperly chilled vaccine was used.
The mistake, referred to as a cold chain failure, happened when children were given a vaccine that was not kept at the right temperature.
Whanganui District Health Board's general manager of service and business planning Tracey Schiebli said the vaccines administered therefore were not effective.
The issue was discussed on Friday at the Community and Public Health committee meeting. Member Judith MacDonald said there was "a strict monitoring criteria for the fridges" the vaccines were kept in.
"If the fridges vary in temperature the policy is you don't use the vaccine."