Three teams have pulled out of the AIMS Games due to measles fears.
This comes as local health agencies are dealing with an increasing demand for vaccinations.
About 11,500 intermediate-aged athletes from 368 schools from around New Zealand and the Pacific are expected to take part in the six-day event from Sunday - the biggest the city has seen.
An AIMS Games tournament spokesman said all three schools that pulled out were from rural areas.
"The withdrawal of several unvaccinated players was more than they could sustain, unfortunately," he said.
So far, more than 50 students have withdrawn from the tournament, he said.
However, not all 50 were related to measles. Some reasons included injury, illness and family bereavement.
It is an increase compared to last year which had 30 withdrawals in the week before the competition because of various last-minute injuries and illnesses.
"For a tournament with 11,500 entries, it's to be expected."
The spokesman said the publicity over the measles outbreak had positive spinoffs as schools had been proactive in getting vaccination certificates and talking through the risks with parents.
AIMS Games organisers were still comfortable with advice from the Ministry of Health and the District Health Boards.
The last advice, two days ago, was that a cancellation was not necessary.
Western Bay of Plenty Primary Health Organisation's manager of general practice services Phil Back said its Hamilton-based regional distribution centre, ProPharma, was receiving orders for 350 vaccines per hour.
"Everyone is doing their best to deal with the demand...," he said.
Back said the Hamilton distribution centre was waiting for extra supply from the Auckland, Manukau head office to keep up with the demand.
"Of the 15 practices from which we have received correspondence, they are collectively waiting for 650 MMR vaccinations to be delivered," he said.
But Back said the practices had no more than 100 MMR vaccinations in stock.
"We are therefore aware that while general practices are doing their best to maintain their stocks of MMR, demand is likely to exceed supply," he said.
Back said the health organisation was working with the Bay of Plenty District Health Board and primary care networks to organise some extra pop-up vaccination clinics.
Details of the times and locations of the pop-up clinics will be made available early next week.