What is causing the number of cases of mumps to increase?

There has been a lot of publicity about mumps recently as reported cases have risen to a 10 year high. There were over five thousand laboratory confirmed cases of mumps reported in 2019. There were probably many more cases than these as many people do not get ill at all, or only very mildly. The increase in numbers of cases has been blamed by the health secretary on the "long term damage caused by anti-vax information". It's not as simple as that. Most of the reported cases have been in young adults who had received the MMR vaccine. The reality is that the MMR vaccine is contributing to the rise in the number of cases in adults.
Before the introduction of the MMR vaccine in 1988 nearly everyone contracted mumps as a child, usually between five and ten years of age, when it was invariably a mild and harmless illness, with many not getting ill at all, which then gave lifelong protection.
Before the arrival of the MMR vaccine there was no demand for a vaccine against mumps. In 1974 the Joint Committee on Vaccination and Immunisation, the body that advises the UK government on immunisation, felt "there was no need to introduce routine vaccination against mumps." Mumps has not become any more dangerous since then. However, a problem with mumps is that it is decidedly more unpleasant, and has more complications, in adults. When virtually everyone contracted mumps as children very few adults contracted the disease. Though complications are rare in children, painful swelling of a testicle occurs in 1 in 4 men (though it is extremely rare for this to cause infertility, if it does at all) and the rare complication of permanent hearing loss is more likely to occur in adults.
The mumps component of the MMR vaccine is relatively ineffective. In a recent outbreak of mumps amongst young adults in Scotland, 84% of those who contracted mumps had received at least one dose of MMR vaccine and 62% had received two doses. There have been similar figures in numerous other outbreaks. Because the protection given by the MMR wears off after a few years, the vaccine is pushing the disease from children into older age groups in whom complications are more likely. Instead of eradicating mumps, the vaccine is turning the disease from a trivial one into a more serious one than it was. The MMR is the problem, rather than the solution. An editorial in the British Medical Journal in 1980 warned of this possibility but the warning was ignored. We are now seeing the consequences of this.
You can find out more about the risks of mumps on our mumps page.
What is the best way forward?
Since the single mumps vaccine is no longer produced, the MMR is now the only vaccine available that offers any protection against mumps. Sadly the protection it offers is likely to fall away over subsequent years and so it is questionable whether any benefits outweigh the risks. The best way forward for a child may be to do nothing and hope that he or she contracts mumps as a child when it is likely to be harmless and give life-long protection. For an adult, especially males, it may be worth considering the MMR vaccine.