Review: Varicella vaccination is effective in childrenPDF
ACP J Club. 2002 Jan-Feb;136:25. doi:10.7326/ACPJC-2002-136-1-025
Skull SA, Wang EE. Varicella vaccination—a critical review of the evidence. Arch Dis Child. 2001 Aug;85:83-90. [PubMed ID: 11466178]
What are the benefits and harms of varicella vaccination in children?
Studies were identified by searching MEDLINE (1966 to 2000) with the terms chickenpox, vaccination, and human and with methodologic terms to retrieve high-quality controlled clinical trials and cohort studies; EMBASE/Excerpta Medica; and the Cochrane Library. The Internet was searched for position papers and summaries from health organizations and vaccine product information, and reference lists of relevant articles were reviewed.
Studies were selected if they were randomized controlled trials (RCTs) or cohort studies of healthy humans vaccinated with varicella zoster virus (VZV) vaccine and they assessed the incidence of varicella, zoster, or adverse reactions to vaccination.
Data were extracted on study design, patient characteristics, length of follow-up, vaccine dose, and outcomes (vaccine effectiveness, adverse reactions, transmission of varicella, and risk for herpes).
10 reports from 8 RCTs assessed vaccine effectiveness: 2 RCTs of a single dose of VZV showed effectiveness in preventing varicella; 1 showed 100% protective efficacy at 9 months, and 1 showed 72% protective efficacy at 29 months. 3 dose-titration RCTs supported the preventive efficacy of VZV. The number needed to vaccinate to prevent 1 additional case of varicella ranged from 6 to 12. One RCT showed no difference in vaccine effectiveness for doses ranging between 439 and 3625 PFU; a second showed effectiveness at doses ≥ 1260 PFU only; and a third showed effectiveness at doses from 7943 to 10 000 PFU. 13 reports from 12 trials assessed adverse reactions; of 3 RCTs of children, none showed an increase in fever or varicella-like rash from VZV over placebo. 1 RCT showed that more vaccine recipients had local reactions than did placebo recipients at 48 hours (27% vs 19%). Injection-site reactions ranged from 7% to 30%. Adverse reactions were not related to vaccine dose. Few trials examined transmission of varicella from vaccinated persons to others; 1 RCT found seroconversion but no disease in siblings of VZV-vaccinated persons. 1 RCT that investigated the risk for herpes zoster in vaccinated persons found no zoster in either vaccinated or placebo groups at 9 months.
Evidence from randomized controlled trials supports the effectiveness of varicella vaccination in children.
Source of funding: Not stated.
For correspondence: Dr. S. Skull, Victorian Infectious Diseases Service, Royal Melbourne Hospital, Parkville, 3050 Victoria, Australia.
Varicella (chickenpox) is a common contagious disease for which we have had a live attenuated varicella vaccine containing Oka-strain virus for several years (1). One of the first target populations was immunocompromised children. Recently, the routine use of varicella vaccine has been considered. The review by Skull and Wang shows convincingly that varicella vaccine is effective in preventing varicella. Achievement of herd immunity is difficult, if not impossible, because vaccinated persons may develop herpes zoster caused by the wild virus. One obstacle against routine vaccination has been the storage of the vaccines. Earlier varicella vaccine had to be frozen, but a commercial product is now available that can be refrigerated. No commercial product is currently available that can be combined with other routine vaccines.
Insufficient knowledge exists about the occurrence of herpes zoster in vaccinated persons as they grow older. However, it seems that zoster is less common among vaccinated persons. It will take several more years, however, before we have evidence of an association.
Vaccination is cost-effective for society, but the cost-effectiveness is not so obvious to the health care organizations that pay the costs of routine childhood vaccinations (2, 3). The review by Skull and Wang shows that varicella vaccine could and should be used more widely than it is. It may be time to implement routine vaccination for all children for varicella.
Matti Uhari, MD, MSc
University of Oulu
Matti Uhari, MD, MSc
University of Oulu