A Vaccine for Varicella at Last!
After nearly six years with the FDA, Merck's live attenuated chickenpox vaccine, Varivax, is finally on sale in the USA - the first country worldwide to approve this particular product (although similar chickenpox vaccines are sold in Japan and Europe).
Varicella develops in up to 95% of children under 12. In childhood, it is usually a self-limiting disease, but in adults and immunocompromised patients, the disease is much more serious. Within the USA, of the less than 100 deaths a year caused by this disease, 50% of these are in adults (even though this group accounts for only 2% of reported cases), and 25% of deaths occur in immunocompromised patients (1). In children who are immunocompromised or who have a malignancy, 7% of clinically apparent cases are fatal and about one third develop disseminated disease (2).
Merck Sharp & Dohme started preliminary work on this vaccine in the mid 1960s and settled on the Oka strain of the virus in 1981 (licensed from Osaka University). However, manufacturing problems, trials to clarify efficacy, and safety concerns acted to delay approval.
Immunocompetent children aged 1-12 years are 70-90% protected against chickenpox by a single 0.5 ml dose, while two such doses four to eight weeks apart are required for adolescents and adults. Immunity usually lasts for at least six years (1). The breakthrough rate in healthy children followed up for two years is less than 1% (3), and vaccinees who develop chickenpox tend to have much milder disease than those who acquire natural infection (4,5). Studies have shown that routine immunization in children would be cost-effective by reducing the number of work days lost by parents (6,7).
The vaccine has been tested in over 11,000 individuals over a ten-year period. The main adverse reactions reported have been tenderness and erythema at the injection site in about 25% of vaccinees and a sparse generalized maculopapular or vesicular rash occurring within one month after immunization in about 5% (1). Fatigue, malaise, and nausea have also been reported (3). The vaccine should not be given to pregnant women and, because of the association between varicella, salicylates, and Reye's syndrome, salicylates should be avoided for six weeks following vaccination.
1. The Medical Letter 1995; 37: 55-57.
Freeze Plantar Warts Twice but Palmar Warts Once
Berth-Jones and colleagues (1) suggest that a double freeze-thaw cycle confers little or no advantage over a single freeze in the treatment of palmar warts, but may be considerably more effective for plantar warts.
In the study, 300 subjects were randomized to one or two freeze-thaw cycles given at three-week intervals. Keratolytic wart-paints were applied throughout the study, and plantar warts were pared prior to freezing. After three months, the only significant difference in cure rate between the two groups was a 24% improvement in the cure rate (from 41% to 65%) for plantar warts given double-freezing.
The authors felt that their results support the theory that curing warts depends on the stimulation of an immune response to the wart virus rather than simple destruction of the cells that contain the virus, and optimal response requires only minimal cell damage.
With plantar warts, sufficient callus remains after paring to be an effective thermal insulator requiring double-freezing.
1. Berth-Jones J, Hutchinson PE. Br J Dermatol 1992; 127:262-5.
Center for Disease Control and American Academy of Pediatrics
Healthy, non-immune children up to 13 years of age should receive one dose of varicella vaccine; infants 12 to 18 months old should preferably receive theirs at the same time as their MMR vaccine. Healthy, non-immune, susceptible adolescents and adults who are at risk of exposure should receive two doses of the vaccine, administered four to eight weeks apart.
2. Marwick C. JAMA 1995; 273: 833-836.
3. Scrip 1995; 2011: 20.
4. Kuter BJ et al. Vaccine 1991; 9: 643-647.
5. White CJ et al. Pediatric Infectious Diseases Journal 1992; 11: 19-23.
6. Huse DM et al. Journal of Pediatrics 1994; 124: 869-874.
7. Lieu TA et al. JAMA 1994; 271: 375-381.