Measles outbreaks will have long-lasting impact

The number of measles cases in the European region tripled in 2018. A total of 82,596 people in 47 of the 53 countries in the WHO’s European region, were infected. The disease killed 72 children and adults in Europe last year.

Europe is not alone. The US says it is in the grip of the worst outbreak in years, the disease has killed 900 people in Madagascar since September, and more than 12,000 people in the Philippines were diagnosed with measles in January and February alone.

But the illness, hospitalisations and deaths caused during these outbreaks could go beyond measles. Most measles sufferers recover from their unpleasant illness. A small number of people infected with the virus can develop SSPE later in life – a fatal brain condition that can occur many years after a measles victim appears to recover from their initial infection.

Immune ‘amnesia’

However, measles infection has also long been associated with higher rates of subsequent illnesses. When the measles vaccine was introduced it led, as expected, to a sharp drop in measles cases. But deaths from other diseases also fell – for reasons which remained a mystery for decades.

In 2015, a paper published in Science offered a new explanation. The researchers found that measles predisposes children to all other infectious diseases for up to a few years. After fighting off measles, the immune system makes a come back but has ‘forgotten’ what it once learned. The child’s immune system has to start afresh, rebuilding immune protection against viruses and bacteria it had previously fought off.

A follow-up study in 2018 identified specific parts of the immune system which are disabled or compromised by measles. The scientists studied unvaccinated children affected by a measles outbreak in a Dutch Orthodox Protestant community (the so-called Dutch Bible Belt where outbreaks are more common than elsewhere in the Netherlands). They found fewer memory B cells circulating in children after the measles outbreak. Their immune systems were showing signs of the ‘amnesia’ described in the 2015 study.  

‘Wakefield’s children’

Most of the studies mentioned above looked at how measles infection affects the long-term health of children. However, not all measles cases are in kids. In fact, one of the paradoxes of Europe’s current outbreaks is that infant immunisation against measles remains strong in most countries. How could Europe have generally good vaccination rates and record measles cases? The answer is simple: many of the cases are in adolescents and young adults. Where children are affected, they are often infants younger than 12 months of age – babies too young for their first of two MMR vaccines.

This cohort of at-risk young people includes those whose parents opted out of recommended vaccines during the late 1990s and early 2000s. Concerned by Andrew Wakefield’s claims that the vaccine was linked to developmental problems, they decided against immunising their children.

Like all parents, they were doing what they believed was best. Some reasoned that their child might not catch measles and, if they did, their chances of survival would be good. Either way, they hoped for the best and presumed the risk had faded away as their child grew up. Now we know otherwise.

Wakefield’s paper has since been withdrawn, his medical license revoked, and his theory thoroughly tested and dismissed by rigorous research. Yet his legacy lives on. Many countries have run catch-up campaigns for those who missed out on infant immunisations in the past, but young people can be hard to reach.

The question now is, how many thousands of young adults who have fought off measles are now at elevated risk of other illnesses? And will we see higher rates of disease in this group in the years following major measles epidemics? If so, which diseases?

Colds and flu, pneumonia and meningitis – only time will reveal the true legacy of Wakefield’s 1998 publication. At this rate, its impact looks certain to run into the next decade and spread beyond measles, mumps and rubella outbreaks.