Wales' chief medical officer has warned of the threat from anti-vaccination campaigners.
In his annual report, Dr Frank Atherton said people needed to be made aware of the benefits of vaccines.
In January, the Royal Society for Public Health said "misinformation" about the safety of vaccines was being spread on social media.
Unicef says more than half a million children in the UK were unvaccinated against measles from 2010 to 2017.
The chief medical officer's report says the rate of two year olds in Wales getting the first dose of the measles, mumps and rubella (MMR) vaccine is below 95%.
That is the rate required to protect a population from a disease, according to the World Health Organisation.
Latest figures show 94.3% of two year olds received the MMR vaccine in Wales - but more than half of local authority areas were below the 95% target.
The lowest proportion was just over 90% in Vale of Glamorgan, but the immunisation programme was doing better on Anglesey and in the south Wales valleys, traditionally more deprived parts of the country.
The highest take-up was in Merthyr Tydfil, with 97.2% of two year olds getting the jab.
"Most people do choose to be vaccinated, but a small minority remain unconvinced by the safety and benefits of vaccines," Dr Atherton said.
"We need to work with clinicians and other experts to ensure that parents are fully informed of the benefits of vaccination, to ensure maximum uptake of the vaccine and achieve our aim of eradicating preventable diseases.
"Similarly older people need to understand the health benefits to them of vaccination against influenza, pneumococcal disease and shingles."
Students were urged to make sure their vaccinations were up to date following reports of cases of mumps at Cardiff Metropolitan University in April.
Last year, Public Health Wales asked parents to get their children vaccinated after outbreaks of measles around south east Wales.
Sonia Davies, a retired nurse and health visitor from Llanelli, told BBC Radio Wales people have become "complacent" about vaccines.
"I would give them all the information I had available, but at the end of the day it is their choice," she said.
"It can be very frustrating indeed, it's not an argument, we are giving them the facts and the facts speak for themselves and all you do is encourage them to reconsider their views.
"People have become very complacent about childhood diseases, they don't realise how serious they can be."