NEW YORK (Reuters Health) - Unlike chickenpox itself, the vaccine against chickenpox does not increase the risk of stroke or brain inflammation in children, according to a large US study reported in the journal Pediatrics.

Stroke is a known complication of chickenpox, a viral disease also called varicella, the study team points out. 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, Dr. James G. Donahue of the Marshfield Clinic Research Foundation, Wisconsin and colleagues analyzed data for the period 1991 through 2004 from the Vaccine Safety DataLink on 3.2 million children, 35.3 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 associated with known risk factors such as sickle cell disease and heart disease, they found.

Donahue and colleagues 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.

"Complementing two recent reviews that found serious adverse events to be rare after varicella vaccination, this study offers reassurance that the rare complication of stroke seen after varicella infection" is simply a coincidence, not a cause and effect relationship, the team concludes.

SOURCE: Pediatrics, February 2009.

Related MedlinePlus Pages:

• Chickenpox
• Childhood Immunization
• Stroke