From the CDC's <a href="http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/meas.pdf" target="_blank">measles pink book</a>:<br><br><div style="margin:20px;margin-top:5px;">
<div class="smallfont" style="margin-bottom:2px;">Quote:</div>
<table border="0" cellpadding="6" cellspacing="0" width="99%"><tr><td class="alt2" style="border:1px inset;">Acute encephalitis occurs in approximately 0.1% of reported cases. Onset generally occurs 6 days after rash onset (range 1–15 days) and is characterized by fever, headache, vomiting, stiff neck, meningeal irritation, drowsiness, convulsions, and coma. Cerebrospinal fluid shows pleocytosis and elevated protein. The case-fatality rate is approximately 15%. Some form of residual neurologic damage occurs in as many as 25% of cases. Seizures (with or without fever) are reported in 0.6%–0.7% of cases.</td>
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1 in 1000 get acute encephalitis. Of those, 25% may have residual neurological damage. So no, 1 in 1000 do not have brain damage. The stat is actually .25 per 1000 or 25 per 100000, or 2-3 per 10000. The pink book doesn't give any more specifics on the range that "some form" of residual neurological damage may take, and I don't have any information on that.<br><br>
To put things in perspective, the pink book quote above says that 15% of the 1 in 1000 who get acute encephalitis will die. This is 0.015% of those who get the measles. The government's <a href="http://www-fars.nhtsa.dot.gov/Main/index.aspx" target="_blank">Fatality Analysis Reporting System</a> estimates that in 2008, there were 12.25 fatalities due to vehicle accidents per 100,000 population, which is equivalent to a 0.012% chance of dying in a car accident.<br><br>
It should also be pointed out that that acute encephalitis is not the same as SSPE:<br><br><div style="margin:20px;margin-top:5px;">
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<table border="0" cellpadding="6" cellspacing="0" width="99%"><tr><td class="alt2" style="border:1px inset;">Subacute sclerosing panencephalitis (SSPE) is a rare degenerative central nervous system disease believed to be due to persistent measles virus infection of the brain. Onset occurs an average of 7 years after measles (range 1 month–27 years), and occurs in five to ten cases per million reported measles cases. The onset is insidious, with progressive deterioration of behavior and intellect, followed by ataxia (awkwardness), myoclonic seizures, and eventually death. SSPE has been extremely rare since the early 1980s.</td>
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