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December 2006 NEW YORK - Preventing varicella was a top story this year – in both pediatric and adult medicine. Earlier this year, the Advisory Committee on Immunization Practices recommended a second dose of varicella vaccine, and just last month, the committee gave the green light for a herpes zoster vaccine to prevent painful shingles in adults. “There’s been an awful lot of activity in the past 18 months for a virus that had been laying low for about 10 years,” said David W. Kimberlin, MD, of the University of Alabama in Birmingham, who spoke at the 19th Annual Infectious Diseases in Children Symposium, held here. In the prevaccine era, there were about 4 million cases of varicella annually, and Kimberlin said the U.S. birth cohort is about 4 million annually, meaning almost everyone got varicella zoster virus. This was problematic, Kimberlin said, because this virus caused somewhere between 8,000 and 18,000 hospitalizations and 100 deaths annually. However, that all changed when the live-attenuated varicella vaccine was added to the Recommended Childhood Immunization Schedule in 1996. According to data published in The New England Journal of Medicine (2005;352:450), there was a dramatic dip of about 82% in varicella-related mortality rates from the prevaccine era to the postvaccine era, and a reduction of about 60% in ambulatory visits related to varicella as well. Jane F. Seward, MD, et al reported an overall decrease of 71% (P=.002) of varicella cases in Antelope Valley, Calif., with a pronounced drop of about 63% in the varicella rate in children aged 5 to 9.
There have, however, been reported cases of breakthrough chickenpox, which could present in a somewhat milder fashion than wild type. Most children with breakthrough disease don’t experience a fever, and most have fewer than 50 pox lesions, which is very different than the wild type, he said. Kimberlin said that many of these breakthrough cases were found in the school setting, where outbreaks occur. These cases of breakthrough illness, coupled with data that noted a marked shift in the age of patients that were getting vaccinated – from toddler age to the adolescent age – led federal health officials to recommend a second dose of varicella vaccine. Kimberlin said this shift in the average age of patients contracting varicella was particularly worrisome for health officials, because adolescents and adults present with the most troubling complications of varicella. “We have this perfect storm brewing in that we are continuing to have outbreaks and the age of patients that are involved in which those outbreaks are occurring is older,” Kimberlin said. About 20% of varicella vaccine recipients fail to generate adequate protective concentrations of antibody with their first dose of varicella vaccine. However, that rate is reduced to almost nothing following a second dose of vaccine, Kimberlin said. Looking at data following the T-cell response, it appears that two doses of varicella vaccine are generating an overall immune response similar to that of wild type illness, he said. According to prospective data published in The Pediatric Infectious Disease Journal (2004;23), the booster dose could be protective against breakthrough illness, in that children who have had two doses of vaccine have a 3.3-fold lower risk for breakthrough illness than those who only received one dose.
Kimberlin cited draft recommendations from the AAP COID, which initially voted in October 2005 to recommend a second dose of varicella vaccine but then worked with the ACIP to coordinate efforts in the recommendation. When the ACIP came onboard in June 2006 with its similar recommendation, the AAP moved forward with preparing its statement. These draft recommendations state that the second dose of varicella vaccine is recommended for children aged 12 months through 12 years of age. The two doses should be administered separately at least three months apart. If the second dose is administered at least 28 days following the first, the second dose doesn’t need to repeat. If the first dose of vaccine was administered at 12 to 15 months, which coincides with the administration of the measles-mumps-rubella (MMR) vaccine, the second dose should be given at 4 to 6 years of age, right before a child enters kindergarten, he said. The draft guidelines also go on to define who may be immune to the virus, noting that people have immunity if they have documented vaccines, a health care provider diagnosis of varicella disease. In those cases of mild illness, a person may be considered immune if an outbreak occurred at the same time of their illness. Kimberlin said there are two vaccines on the market for varicella, the monovalent varicella vaccine (Varivax, Merck/Oka), which is approved for use in children aged 12 months and older, and the newest formulation, the MMR-varicella vaccine, (MMRV, Proquad, Merck) which is approved for people aged 12 months through 12 years. The first vaccine to prevent shingles, Merck’s Zostavax, was recently approved in both the United States and Europe for adults aged 60 or older. Shingles develops when the virus that causes chickenpox, varicella-zoster, is reactivated. After a childhood bout of varicella, the virus lies dormant for many years, ready to come into action when the carrier’s immune system weakens either through age or illness. Discussing postexposure prophylaxis options, Kimberlin said that VariZIG (Cangene Corp.) was approved for as an investigational new drug in February. The product will be distributed by FFF Enterprises, which also distributed VZIG. He said this is a different situation because it is under IND, so it is now an expanded access program that has central internal review board approval. Specifically, the western IRB has approved this particular research protocol. Unlike VZIG, informed consent must be obtained before giving VariZIG to patients.
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