The Kaitaia GP, and 2014 New Zealander of the Year, hit the headlines after disrupting the viewing of the film in Kaitaia on Monday night, telling the audience their mere presence "will cause babies to die".
Dr O'Sullivan spoke of the negative outcomes he had seen among non-immunised children and others in the community.
He pleaded with other health professionals to leave the film viewing organised by anti-vaccination group WavesNZ, fronted by Tricia Cheel.
Ms Cheel told the Northern Advocate she believed Dr O'Sullivan had been intimidating, and "finger pointing".
But he said he only raised his voice during the haka, before he gave his short address about how vaccines save lives.
"I did call out the other health professionals in the audience, asking what they were doing there when their job is to keep people healthy."
Before the screening, Dr O'Sullivan had been outside asking people not to go in when Ms Cheel confronted him.
Ms Cheel later told the Advocate that other health providers in Kaitaia were afraid to fall out with Dr O'Sullivan because of his influence and the health funding he attracted to the district.
Dr O'Sullivan said he had not worked with other doctors or clinics for years.
"You would have to ask them how they feel,'' he said of her claim.
He said he had never met Ms Cheel before or "seen her around", and was not sure how knowledgeable she was about the local health sector.
Dr O'Sullivan has been outspoken for many years about the need for immunisation, especially in the Far North where vaccination rates are low and incidents of serious health issues due to the effects of those diseases are high.