With New Zealand experiencing its worst measles outbreak in decades, the message from the authorities has been unanimous - get vaccinated if you aren't already.
But the two-course MMR jabs are delivered at ages 15 months and four years - not all of us can remember back that far or have the documentation handy.
The Immunisation Advisory Centre says it's better to get a jab than rely on a faulty memory.
Here's what to do if you're not sure whether you're protected.
Born before 1969
If you were born before man stepped on the moon, chances are you were exposed to the virus as a child and have a natural immunity.
"Prior to that, measles was a rite of passage in childhood - pretty much everybody had it," University of Auckland vaccine researcher Helen Petousis-Harris told Newshub.
The current outbreak backs that up, with few cases recorded in over-50s.
"When you look at the cases by age, there's almost nobody older than 50 that's been reported as a case."
Born after 1969, before 2005
"Once the vaccine came in, you started to see a lot of people didn't get measles - but because we didn't immunise that well, a lot of people didn't get vaccinated," said Dr Petousis-Harris.
The current outbreak has hit those in their 20s the hardest, as the graph above shows. There was no national immunisation database between 1969 and 2005. Dr Petousis-Harris said people born between those years should ask their parents or check their Well Child/Plunket book, if it was available, which should contain details of their immunisations.
Another possibility, particularly if you've been with the same doctor since childhood, is to ask them to look it up.
"There's a lot of people who don't have those options. [For them] it's quite simple - go and get the vaccine. It doesn't matter if you've had one, two or even three doses in the past... just go and have one."
The Ministry of Health says some jabs done before 2005 will be in the NIR.
Born 2005 or after
Everyone born in New Zealand after 2005 has had their details entered into the National Immunisation Register (NIR) - it's as simple as asking your GP or the NIR administrator at your local district health board to look it up.
People who have arrived in New Zealand after 2005 may also have their status in the NIR.
"If people have come in from overseas, often their practice will enter the information," said Dr Petousis-Harris. "There will very likely be records there."
What to do if you're not vaccinated
"It's pretty simple - if you don't know, go and get a vaccine," said Dr Petousis-Harris.
If you didn't get immunised as a child for health reasons, there's a chance you could be exposing yourself unnecessarily.
"A lot of people don't get vaccinated because they're perceived to be contraindicated - they're perceived to have a condition that should prevent them from getting the vaccine, and that's often not the case," said Dr Petousis-Harris. "So it is definitely worth revisiting, because it does depend on the condition."
Newshub.
