Fourteen thousand does of the measles, mumps and rubella (MMR) vaccine are now being distributed to Christchurch general practices as the number of confirmed cases of measles has risen to 28 nearly three weeks after the outbreak began.
Eighteen-thousand doses of the vaccine have arrived in Christchurch from Auckland to top up dwindling supplies and another 9,000 doses are expected to arrive tomorrow.
The Canterbury District Health Board says it has to prioritise the most vulnerable.
Medical Officer of Health Dr Ramon Pink says people aged one to 28 who have never been vaccinated are the target for these vaccines.
Next in line will be unvaccinated people aged 29 and above followed by people needing booster shots.
Dr Pink said medical centres have been very busy prioritising patients for the vaccine while awaiting the arrival of the extra supplies.
"We have a strong coverage of our under five age group and I think this has afforded significant protection," Dr Pink told media this afternoon.
"We are also very aware that one MMR vaccine does provide 95 per cent coverage for our population. And the second dose of the vaccine is for that small percentage who do not gain immunity from that first vaccine," he said.
Dr Pink said research shows that the vaccines that were delivered from 1969 to 1990 "did indeed afford that age group from 29 to 50 years of age really good immunity".
As well as 28 confirmed measles cases as of late this afternoon, Dr Pink said around another 20 cases are being investigated.
He said this shows the primary care community is on high alert for measles cases.
The confirmed cases include cases at two schools.
Dr Pink said there have been seven cases of people with measles being hospitalised and two were in intensive care, but all those cases have recovered and been discharged from hospital.
Two measles cases were confirmed in Auckland this afternoon but authorities say they are not considered linked to the Canterbury outbreak.
Dr Pink said measles is not endemic in New Zealand and travellers coming into the country are the likely source of the Auckland cases.