Parents of small children can now get them vaccinated at the pharmacy.
From Monday, pharmacists are permitted to give vaccines to children under five - something they were already allowed to do for older children and adults.
University of Auckland academic and Immunisation Advisory Centre director Nikki Turner said the number of people taking up the opportunity was expected to be small to start with.
Immunising small children was quite different to immunising adults, and pharmacists would take some time to upskill.
However, the change in rules would make childhood immunisations more accessible over time, she said.
Te Whatu Ora Health NZ sought the rule change to try and boost lagging immunisation rates.
It asked for pharmacists to be allowed to vaccinate babies from six weeks of age for all the free childhood immunisations on the New Zealand vaccination schedule.
Immunisation rates were the lowest they had been in years, it previously told Pharmac, at 83 percent for the general population and 70 percent for tamariki Māori.
Immunisation Advisory Centre general manager Loretta Roberts said the move would make it easier for those struggling to afford or book a doctor's appointment.
"Pharmacies are open often longer hours, on weekends as well so it will give an opportunity for people to find another time to get their children immunised," she said.
It was also expected to help families in remote areas.
"It's very difficult at times to get into GPs, so it gives another access opportunity especially where we've got a lot of patients where we don't have a large number of GPs."
Pharmacists who had decided to offer vaccinations for under-fives had completed extra training administered by the centre, Roberts said.
It was important that whānau still enrolled their child with a GP so they could receive routine health checks, among other support, Turner said.
"This should not be an isolated issue just to go to a pharmacist, it's really important our children are enrolled and have a good relationship with their general practice - it's absolutely vital."