THE outcome is simple. A child who isn’t vaccinated will be susceptible to
measles, mumps and rubella. All three can have serious complications. The main
one is encephalitis, where the virus gets into the brain.
The risk of encephalitis is around 1 per 1000 cases for measles and for
mumps, and around 1 per 6000 for rubella. Up to 50 per cent of children who get
encephalitis are left with permanent brain damage.
Measles kills around 1 in 5000 children in developed countries, and can also
cause SSPE (subacute sclerosing pan-encephalitis) in around 1 in 14,000 cases.
SSPE progressively destroys nerve cells in the brain, leading to mental
deterioration and death.
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The other big risk comes later in life. Mumps and rubella both increase a
woman’s risk of miscarriages, and rubella also causes birth defects, including
blindness, deafness and autism.
Overall, the combined risk from measles, mumps and rubella (if a child were
unlucky enough to catch all three) would be around 1 in 500 of encephalitis, 1
in 14,000 of SSPE and 1 in 5000 of death.
But what chance does your child have of catching these diseases? Parents who
choose not to vaccinate their own child while hoping that everybody else will
may be making a big mistake. There is a certain level of protection, called
“herd immunity”, that has to be maintained to stop a disease spreading.
For measles and rubella this is between 80 and 90 per cent. MMR vaccine
coverage in Britain has now dropped to 88 per cent, so has reached the critical
level (see Graph).
Already outbreaks of infection are occurring in pockets of
unvaccinated children.
Since November 1999, 103 cases of measles have been reported in a religious
community in Salford, near Manchester. Coverage in the area had dropped to
around 80 per cent. And Northern Ireland, where coverage is down to 76 per cent,
is suffering its worst outbreak in seven years.
There are risks associated with the MMR vaccine, as with any vaccine, but the
risks from the diseases themselves are far greater.
The results of several large studies
(see “Triple trouble”)
suggest that MMR causes about
four adverse reactions per 100,000 doses. The most common adverse effects are
mild and include tenderness, slight fevers and rashes.
More serious consequences include seizures, allergic reactions and
anaphylactic shock. There is a 1 in 3000 risk of a child having a seizure, and a
1 in a million chance of anaphylactic shock. However, all of the children in the
studies recovered, and no deaths have been reported.
But there is also still a risk of catching measles, mumps or rubella, as the
MMR vaccine is only about 90 per cent effective. This is one reason why two
doses are given, and after both doses about 1 per cent of children remain
susceptible. So a parent who does not vaccinate their child leaves these other
children at risk too.
Separate vaccines against measles, mumps and rubella ultimately give children
the same level of protection as MMR and the same risks of adverse effects. But
it is riskier in the short term, because it takes longer and children are more
likely to catch measles, mumps or rubella before they’ve had all three jabs.
