by Jorge Vargas, MD

Children who are candidates for a liver transplant, and their siblings who have not yet had the chicken pox, should ALL be vaccinated before a transplant.

C.L.A.S.S. Notes, Spring 1996 -- Most of the time, varicella (chicken pox) is a very benign and mild disease. In some cases, however, children in particular may become severely ill from this highly contagious viral infection. Chicken pox occurs year around with no major seasonal variations; however, it is mostly seen from January to May. In this country, almost four million cases occur every year and between four to nine thousand cases require hospitalization. In a very small number, the infection proves to be fatal.

Severe complications of varicella include pneumonia, encephalitis and other bacterial infections, and may occur in normal, healthy children. Obviously, children who are taking medications to suppress the immune system or undergoing chemotherapy are at a higher risk of developing more severe infections or complications. It was with this group in mind that a vaccine was developed which has proved to be very efficacious.

This vaccine is generally recommended for toddlers between ages 12 to 18 months who have not had chicken pox, as well as older children, adolescents, and adults who may be exposed. Although the vaccine does not provide 100% protection against varicella, cases that occur after vaccination are generally very mild. Several studies have addressed the issues of the length of immunity, which is not permanent, and on the safety and need for booster doses of varicella vaccine 4 - 6 years after the initial immunization.

A major discussion is underway because of the lack of good data on the safety of the vaccine in children receiving immunosuppressive agents. Studies have been carried out in countries like Canada, Japan, and the European Union, and the results are being analyzed. There are studies showing the safety and efficacy of the vaccine in children with debilitating diseases, or children who receive chemotherapy. The Academy of Pediatrics is developing clearer policies and better guidelines for the use, schedule and need of monitoring regarding the efficacy of the vaccine. But it is important to understand that at this point in time, children who are potential candidates for a liver transplant, children who are already on a waiting list for transplantation and their siblings who have not had chicken pox, should ALL be vaccinated before a transplant.

Varicella virus has an incubation period of 11 days to three weeks. Even before the infection is apparent by the presence of skin lesions, it is transmitted in the air by respiratory particles and secretions. Patients are most infectious during the 24 hours before the skin lesions appear and until all lesions are dry and crusted-over completely.

If a child has not had the vaccine or the illness and is receiving immunosuppressive agents to prevent rejection of a transplanted organ, and this child comes in close (and I emphasize close) contact with a child who subsequently develops chicken pox, it is advisable that the child receive a special dose of antibodies to fight the potential infection, to be administered within 72 hours of the contact. This is a specific antibody against the varicella virus called VZIG, and it is given by intramuscular injection in an amount proportional to the child's weight. It is not 100% efficacious, but administered on time may completely prevent the disease or make it much milder. These antibodies, as they were not actively produced by the patient, do not last and only cover a period of approximately 5 - 6 weeks, making it necessary re-administer the treatment in cases where new contact occurs beyond this time.

If a child on immunosuppressive agents develops the disease, we always suggest treating the child in the hospital with intravenous medications designed to kill the virus. We also reduce the amount or dose of immunosuppressive agents while the disease is active, and keep a close eye on potential complications and treat them quickly as they are presented. Frequently an antibiotic treatment for bacterial infections of the skin lesions is also prescribed.

Lastly, having the infection generally confers a child or patient with sufficient immunity to be protected for life. However, in patients whose immune system is depressed by medications, this is not always the case. It is not rare to see either recurrence of the chicken pox or recurrent episodes of the so-called "shingles," which is caused by the same virus.

Dr. Vargas is an associate professor of pediatric gastroenterology/nutrition at UCLA Medical Center and a member of the C.L.A.S.S. Scientific Advisory Committee.