ATLANTA — Intravenous immune globulin should be the primary means of postexposure prophylaxis among persons at high risk of severe varicella complications if there is a shortage of varicella zoster immune globulin, according to a vote by the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices.
This decision was made in the face of looming shortages of varicella zoster immune globulin (VZIG), which may begin as early as next month, when the sole U.S. manufacturer, Massachusetts Public Health Biological Laboratories, closes its plasma fractionation facility, said Dorothy Scott, M.D., of the Food and Drug Administration's Center for Biologics Evaluation and Research.
Among the factors favoring the use of intravenous immune globulin (IVIG) for postexposure prophylaxis is the fact that it usually is in ample supply, said Philip LaRussa, M.D., of the division of pediatric infectious diseases, Columbia Presbyterian Medical Center, New York City. Current IVIG has good antivaricella titers, with 3–8 mL/kg required.
The use of IVIG also permits the window for prophylaxis to be extended, because the peak level is reached much more quickly than with VZIG, within 24 hours, Dr. LaRussa said.
But there are concerns as well. IVIG is not titered for antivaricella antibodies, so there may be some variation in efficacy, Dr. LaRussa said.
“Also, this is going to be a moving target because as we do a better and better job with immunization, and donations made by adults with natural varicella immunity are replaced by those with vaccine-induced immunity, we may have to use more.”
Prophylaxis is recommended for:
▸ Immunocompromised patients without evidence of varicella immunity.
▸ Neonates whose mothers develop symptoms 5 days before to 2 days after delivery.
▸ Premature infants born before 28 weeks or weighing 1,000 g or less who were exposed during the neonatal period and whose mothers do not have evidence of varicella immunity.
For pregnant women, ACIP's measles-mumps-rubella-varicella working group recommended administration of IVIG or close monitoring and treatment with acyclovir if signs or symptoms of illness develop, said Mona Marin, M.D., of the working group.
The recommended dose of IVIG is 400 mg/kg, and it should be administered as soon as possible after exposure and as late as 96 hours after exposure.
Any patient to whom IVIG is administered should subsequently receive varicella vaccine provided it is not contraindicated, but vaccination should be delayed at least 8 months.
An antiviral such as acyclovir also can be used for prophylaxis, in a dosage of 40–80 mg/kg per day for children and 800 mg five times a day for adults. The preferred time for administration is 7–10 days after exposure and for a total of 7 days of therapy, Dr. Marin said.
As with IVIG, in patients given acyclovir for prophylaxis, varicella vaccine should be administered at a later date if not contraindicated and if the patient did not develop varicella disease, Dr. Marin said.
The FDA continues its efforts to restore a supply of VZIG, which remains preferred for prophylaxis when available.
One company has expressed an interest in manufacturing it, “and while we are not allowed to comment on a pending submission, we will do everything we can to make it available under [the Investigational New Drug protocol] as soon as possible,” FDA's Dr. Scott said. “It's conceivable that we will have a licensed product, but possibly not by January,” she said.