Epidemic influenza. Patterns over 20 years (1949-1968).
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005194:Family Practice; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human / Q000453:epidemiology*; D008131:London; D008875:Middle Aged; D012189:Retrospective Studies