Parents turned out with their children in the cold and rain for the clinic on Tuesday.
A total of 28 confirmed cases of hepatitis A have been recorded in mid-Canterbury since April, compared with the normal level of one or two cases a year.
A medical officer of health, Alistair Humphrey, says four adults and a child were hospitalised with the liver-damaging virus.
Dr Humphrey says those people have recovered but an extra effort is needed to prevent the rise in cases of the notifiable disease.
He says good hand washing by everyone after using the toilet will also help stop the outbreak.
Tuesday's clinic was the first of six before 23 October for one to four year olds to rid mid-Canterbury - Ashburton, Methven and Rakaia - of the virus.
Extra nurses and public health staff were brought in from the West Coast and Timaru.