Fatal measles complication 'much more common than thought'
A terrifying and deadly measles complication that kills children years after they have fallen ill is far more common than previously thought, doctors have warned.
Scientists say they are alarmed at the discovery that the neurological disorder, which is always fatal, may affect up to one in 600 non-vaccinated infants under a year old who get measles.
The condition, subacute sclerosing panencephalitis (SSPE), was once considered extremely rare, posing a risk to just one in 100,000 children with a history of measles.
Recent research from Germany updated the incidence to one in 1,700 among children infected before the age of five.
Now a new US study has shown the danger to be much more real for infants, with as many as one child in 600 being affected.
The only certain safeguard against SSPE is universal vaccination, experts stress. With enough of the population immunised, the spread of measles would be contained well enough to protect infants too young to receive the vaccine.
Lead scientist Professor James Cherry, from the David Geffen School of Medicine at the University of California, Los Angeles, said: "This is really alarming and shows that vaccination truly is life saving.
"Measles is a disease that could be eliminated worldwide, but that means vaccinating at least 95% of all who are eligible with two doses of measles vaccine in order to protect everyone, including those who aren't old enough to get the vaccine."
Measles commonly causes a fever, runny nose, cough, red eyes, sore throat and a distinctive rash.
The virus responsible for the infection is usually cleared from the body within 14 days. But in rare cases it spreads to the brain, where it can lie dormant for years - sometimes decades.
Scientists do not know what causes the virus to reactivate, but when it does the result can be SSPE - a horrifying condition leading to memory loss, mood changes, involuntary jerking movements, muscle spasms, and occasional blindness.
Eventually patients may become comatose or enter a persistent vegetative state. Death is inevitable as a result of fever, heart failure, or the brain's inability to control vital organs.
Prof Cherry's team identified 17 cases of SSPE in California between 1998 and 2016, all of which involved patients who had contracted measles as children before being vaccinated.
The average age at diagnosis was 12, but the age at which the disease struck varied enormously, from three to 35.
A follow-up analysis showed that one in 1,387 children who got measles before the age of five, and one in 609 infected when they were less than a year old, went on to develop SSPE.
Many of the victims had ongoing mental or movement problems before they were definitively diagnosed.
Vaccinating a very high portion of the population ensures "herd immunity", meaning that even those who cannot be vaccinated are shielded from infection.
The combined measles, mumps and rubella (MMR) jab is not recommended until infants are about 12 months old because up to that age they retain some of their mothers' antibodies. This reduces the vaccine's effectiveness.
Vaccination may also not be possible for certain individuals with immunological disorders.
In the UK, the first dose of MMR is usually given within a month of a child's first birthday. Because there is a small risk of the vaccine failing, children receive a second injection before they begin school.
Measles is so contagious that 95% of people need to be vaccinated with two doses to protect the 5% who are not immunised.
Prof Cherry said parents of infants who have not yet been vaccinated should take steps to avoid their children being infected - for instance, by postponing trips to countries where measles is endemic.
"It's just not worth the risk," he added.
The research was presented at IDWeek 2016, a meeting of infectious disease experts taking place in New Orleans, US.
A controversial and discredited study published in The Lancet journal in 1998 linking the MMR vaccine with autism led to a sharp drop in vaccination rates in the UK.
Between 1996 and 2002, MMR uptake fell from 92% to 84%, heralding a worrying increase in the number of children contracting measles.
In 1998 there were 56 confirmed cases of measles in the UK. During the first five months of 2006 there were 449.
Dr Andrew Wakefield, the lead author of the 1998 study, was accused of manipulating evidence and having conflicts of interest. In 2010 he was struck off the medical register by the General Medical Council.
Multiple investigations by other experts found no link between the MMR vaccine and autism.
Vaccination rates now appear to have bounced back. Latest figures for the last quarter of 2015 show that 92% of UK children have had one MMR dose by the age of two.