Home-based vaccinations are closing the gap vaccination rates of eight-month-old babies across all socio-economic groups and ethnicities, the Health Ministry says.
Ministry chief advisor for child and youth health Pat Tuohy said the rollout of a programme offering vaccinations in the home had helped raise immunisation rates to 93 percent or higher.
That was across all ethnicities, including Maori and Pasifika children, who had had historically lower rates compared to Paheka and Asian children. There had also previously been a gap between poorer and richer children.
"For some families who are unable or unwilling to attend a general practice to get immunised, we're able to provide immunisation in the home or in another setting that suits them," he said.
The ministry set a target two years ago for 95 percent of all eight-month-old babies to be immunised by the end of 2014.
Meanwhile, whooping cough vaccinations for older children and adults could be introduced following new research into the vaccine's effectiveness, Dr Tuohy said.
A milder version of the vaccine was introduced in 2000 to counter a decline in immunisation rates after many parents were put off by the side effects of the original vaccine.
However, the newer vaccine was not as effective as the original, making it more difficult to prevent outbreaks of the disease, he said.
The study would determine if more booster shots should to be added to the free vaccination schedule.
"Would there be any benefit in providing adults with whooping cough vaccine over time? We don't quite know the answer to that.
"So these are some of the outcomes that we would expect the research to tell us about."
It was possible a whooping cough booster could be combined with tetanus boosters currently given at 45 and 65 years of age.