Immunity to varicella zoster virus in children with leukaemia.

A total of 46% (32/70) of children with acute lymphoblastic leukaemia presenting to the Hospital for Sick Children had a past history of chickenpox. When their immunity to varicella zoster virus (VZV) was assessed, 75% (24/32) had a positive lymphocyte transformation response to VZV antigen in tissue culture while 78% (25/32) possessed IgG antibody against VZV. Therefore, at least 22% of the children were probably susceptible to infection with VZV inspite of having a history suggestive of chickenpox. Of those with a negative or uncertain history 34% had a positive lymphocyte transformation response, while 55% (21/38) had IgG antibody against VZV. Therefore, about one in two of those with a negative history to VZV had some form of immunity to VZV. Hence, regardless of their VZV infection history, children with leukaemia would need to undergo both cell mediated and humoral immunity tests before they may be considered for immunisation with the live varicella vaccine. From our studies, 34% (24/70) of our patients did not have any evidence of immunity to VZV by either test method. These would be considered for immunisation with the live varicella vaccine.