London - Parents have become complacent about vaccinating their children because they have forgotten the impact of devastating diseases, experts warned on Wednesday night.
Many people have no idea what illnesses such as measles, polio or diphtheria could do to children because vaccination campaigns wiped them out generations ago.
Yet many of these viruses are still circulating abroad and could return amid falling uptake of childhood immunisations such as the MMR jab, doctors warn.
Dr Charlie Weller, head of vaccines at the Wellcome Trust, said: "Like many, I grew up in an environment where I didn’t see polio, rotavirus or diphtheria.
"These critical diseases really can take your life or have a devastating impact on health, but they are out of our minds now. Complacency comes about when you don’t remember."
She said vaccination programmes have become "a victim of their own success".
"If you are ill and given a drug that cures you, you remember that," Dr Weller added. "But with a preventative vaccine you never see the disease in the first place, so you don’t necessarily recognise what an amazing prevention this is. That breeds complacency."
Diphtheria – a highly contagious virus that can cause breathing difficulties and paralysis – was eradicated after a vaccine was introduced in 1942.
But experts warn that because diphtheria is so infectious, there is a risk of larger outbreaks if vaccination levels fall.
In the early 1990s, for example, there was a huge outbreak of diphtheria in the former Soviet countries after the break-up of the USSR, with 157 000 cases and 5 000 deaths in an eight-year period.
The USSR previously had a well-run vaccination programme but in the chaos after its collapse immunisation rates fell and disease spread.
Dr Robin Nandy, chief of immunisation at Unicef, said: "People have forgotten how dangerous these diseases can be.
"If you look at younger doctors in high-income countries, they have not seen outbreaks of measles killing children in large numbers."
Professor Jonathan Ball, from the University of Nottingham, said: "The reason that rates of immunisation have fallen is complex.
"Some of it is down to misinformation of vaccine dangers that still do the circuit on social media, and some communities have consistently been difficult to engage with.
"But I suspect much of it is down to the fact that we have forgotten how serious these infections can be and have started to think of them as simply trivial childhood infections."