Larger people with high body fat percentages need longer needles so their Covid-19 vaccinations make it deep into their muscle.
But there is no exact criteria in New Zealand saying who needs this and who doesn't - it's up to vaccinators decide.
That's prompted a warning from one woman who said she would have been injected with a short needle if she hadn't said something.
Academic Cat Pausé said she was grateful to have had her first dose last week, but it didn't entirely go to plan.
"When the vaccinator was preparing to give me my shot, they did not know that for fat people and especially super-fat people like me, they needed to be using a longer syringe to give the vaccination."
She knew she needed something different and was inoculated with a 38mm needle instead of the standard 25mm one, but it made her wonder how many members of the public - and indeed vaccinators - know how best practice caters for larger people.
Pausé said people like her are part of 'the team of five million' but, in her opinion, large body types are not always thoroughly considered in healthcare.
"Most fat people are used to - when they go to the doctor - they have to request the bigger cuff for the blood pressure machine because it's not just in the room by standard. They have to request the extra-large gown because that's the only gown that can provide them privacy, but again that's not in the room by standard. This is a very common experience for fat people because the world is not built for us."
She has written to Covid-19 Response Minister Chris Hipkins to ensure that all vaccinators know to cater for all body types and is warning others to double-check when they get their shot.
Jane Morphet, the clinical Covid-19 education manager at Aotearoa's Immunisation Advisory Centre, told RNZ our vaccinators had been trained from square one to use the longer injections when needed.
"We are really keen to make sure that the vaccine does reach the muscle. If you have somebody that's got a very large arm and you're injecting into that, it's possible you could just go into the subcutaneous fat and not the muscle. And if that were to happen you might have get a suboptimal - less of a response - to the vaccine."
Vaccinators should always have longer needles on hand and they are trained to be discrete about upping a needle size.
Morphet said researchers had started looking into the difference a longer or shorter needle made because there was not a lot of evidence around the issue at the moment.
"But if in doubt, we always advise people to use the longer needle. It will never do any harm to have a slightly longer needle and it doesn't hurt any more, which is the bit that people have a misconception about."
There is no exact threshold for the two needle sizes in New Zealand and the Ministry of Health said it was up to the vaccinator to assess.
New Zealand Health Survey data shows Māori and Pasifika are more likely to have high BMIs than other ethnicity's in New Zealand.
Māori health academic and GP Dr Sue Crengle said there was no harm in asking about the best tool for your body type.
"I would really encourage - if you know that you've got a little bit more of a covering than other people - that you actually ask to get the longer needle. And it's completely within your right to do so, and it would be absolutely the right thing to do to make sure the vaccine works as well as possible."
As of last month, 7666 people had completed Covid-19 vaccinator training in New Zealand, on top of the regular workforce of GPs, pharmacists and the Defence Force.