The Japanese Committee for the National Registry of Subacute Sclerosing 
Panencephalitis (SSPE) confirmed that 215 cases of SSPE occurred in the 20 years 
from 1966 to 1985, as discovered in the 10-year surveillance from April 1976 
through March 1986. The annual incidence in recent years has been between 10 and 
23 cases. Among cases with a certain history of measles illness or measles 
vaccination, 184 (90.2%) had a history of measles illness without receiving 
measles vaccine. There were 11 probable measles vaccine-associated cases (5.4%), 
three (1.5%) being vaccinated with a combined use of killed and live vaccine and 
eight (3.9%) with further attenuated live vaccine. There were nine cases (4.4%) 
without a history of either measles illness or measles vaccination. Intervals 
between measles illness and the onset of SSPE varied from 1 to 16 years (mean, 
7.0 years). The periods following measles vaccination with further attenuated 
live vaccine were 2 to 11 years (mean, 4.6 years). Annual incidence rates of 
SSPE per million cases of measles ranged between 6.1 and 40.9 (mean, 16.1) in 
the 10 measles epidemic years 1968-1977, and those following vaccination with 
further attenuated live vaccine were zero in most years and at the highest 3.08 
(mean, 0.9) per million doses of distributed vaccine.