By choosing to take their children out of vaccination programmes, parents are risking increasing the risk of transmitting otherwise preventable diseases.
Roberto Bertollini, the WHO's representative to the EU, has voiced concerns that this so-called 'vaccine hesitancy' is becoming a serious problem across parts of Europe.
The problem is so acute the journal ‘Vaccine’ has published a special edition on WHO recommendations on vaccine hesitancy.
The issue has arisen because many parents continue to believe that certain vaccines may cause serious developmental problems in their children. These unfounded fears lead parents to opt their children out of vaccination programmes.
Bertollini blames spurious claims that linked the measles vaccine with autism published in the British medical journal ‘The Lancet’ a number of years ago. Despite the fact that the link has long been discredited and the article withdrawn, the myth persists. The vaccines in question have been shown to be clinically safe.
"WHO is concerned about mistrust in vaccination programmes among some population groups," warned Bertollini, who earlier this year urged members of the European parliament to make policy decisions based on solid science.
There is a pressing need for EU member states to follow up on their 2014 commitment to close the immunisation gap by implementing the WHO-led European vaccine action plan. That way, all citizens could hope to enjoy life free from vaccine-preventable diseases.
While parents may worry unduly about the risk to their own children, the concerns - and consequences - of avoiding vaccines are much wider and much more serious.
Recent events in Germany show how quickly the problem can take hold. There, a child from Bosnia & Herzegovina, where measles is virtually endemic, spread the virus to the local population.
A child on a school visit from France to Berlin contracted the virus. Subsequently, 47 unvaccinated children from the French school also developed the disease.
Other cases in Sweden, Croatia and Austria have been linked to the German outbreak. In Austria, there were outbreaks in seven of its nine provinces, with 24 people hospitalised.
Authorities said that five of the cases were imported, including two from Germany and two from Bosnia & Herzegovina.
In the 12 months to April 2015, 46 per cent of all cases of measles reported to the European centre for disease prevention and control (ECDC) - more than 1800 recorded infections - were in Germany.
Vaccines are most effective when they cover the vast majority of the population, conveying what is known as 'herd immunity'. In the case of measles, if 95 per cent of the population receive two doses of the vaccine, then the disease struggles to spread.
In short, the lower the coverage, the greater the risk of contagion. Vaccine coverage can be poor for many reasons; in less well-off countries, cost is an issue.
In a number of affluent societies, parents are choosing to opt out, thinking they can better protect their children.
However, the consequences are the same - a greater risk of the virus spreading - but here the problem is eminently avoidable. This is why Bertollini is worried that some parents are putting both their own children and their fellow EU citizens at greater risk.