Unlike chickenpox itself, the vaccine against chickenpox does not increase the risk of stroke or brain inflammation in children. Stroke is a known complication of chickenpox, a viral disease also called varicella. Although there have been case reports of stroke after varicella vaccination, the existence and magnitude of any vaccine-associated risk has not been determined. To shed light on this subject, researchers from America analysed data for the period 1991 through 2004 on 3.2 million children, 35 percent of whom received the varicella vaccine. They identified a total of 203 new stroke cases, including 8 that occurred within 12 months of varicella vaccination. However, the timing of each case did not suggest that vaccination caused the strokes. Stroke was strongly found to be associated with known risk factors such as sickle cell disease and heart disease. The researchers also identified 243 cases of brain inflammation or encephalitis. None of these cases occurred during the first 30 days after vaccination and there was no association between encephalitis and varicella vaccination at any time in the 12 months after vaccination. The above study offers reassurance that the rare complication of stroke seen after varicella infection is simply a coincidence and not a cause and effect relationship.
Pediatrics
January 2009