A Ministry of Health spokeswoman said the October 1 change had been widely communicated to providers over recent months to ensure they were letting families know.
"Most parents and caregivers find out information about their children's upcoming immunisations from their general practice teams, Plunket and other Well Child Tamariki Ora providers, and updated ministry resources about the immunisation programme or the ministry website," she said.
The vaccination was safe and effective at 12 and 15 months and meant children were protected as soon as possible, she said.
Over the coming months general practices would contact parents and caregivers of children older than 12 months to make sure their children were up to date with the new schedule.
She said there was only a four-week gap required between doses so children could be quickly caught up.
Royal New Zealand College of General Practitioners communications adviser Emma McCleary said the organisation was aware of the change and had informed its 5500 members in the weekly newsletter on September 29.
"Our e-newsletter is our primary channel for communicating with GPs. We sent them detail of the schedule change that was provided from the Ministry of Health as well as a key message sheet."
She said GPs routinely called or texted parents to remind them of upcoming immunisation dates.
Auckland mother Tahnya Goodall supported the change but only found out when a friend stumbled across the new schedule online.
She contacted her GP about the change and what it meant for her 13-month-old son Kheit and arranged for him to have the 12-month vaccinations this week.
Goodall believed the changes needed to be better publicised but acknowledged it was a difficult time to implement such a change.
A scheduled Plunket appointment was cancelled during the level 4 lockdown and she had not been contacted since.
"Plunket are between a rock and a hard place," she said of the timing. "GPs are relying on Plunket and Plunket is relying on GPs.
"The change is good. It keeps them and everyone else around them protected earlier, especially if they attend daycare."