Infectious Diseases| November 01 2004 Contagiousness of Varicella in Vaccinated Cases AAP Grand Rounds (2004) 12 (5): 61. https://doi.org/10.1542/gr.12-5-61 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Contagiousness of Varicella in Vaccinated Cases. AAP Grand Rounds November 2004; 12 (5): 61. https://doi.org/10.1542/gr.12-5-61 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search nav search search input Search input auto suggest search filter All PublicationsAll JournalsAAP Grand RoundsPediatricsHospital PediatricsPediatrics In ReviewNeoReviewsAAP NewsAll AAP Sites Search Advanced Search Topics: chickenpox, human herpesvirus 3, vaccination Source: Seward JF, Zhang JX, Maupin TJ, et al. Contagiousness of varicella in vaccinated cases: a household contact study. JAMA. 2004;292:704–708. Household transmission studies performed prior to licensure of varicella vaccine and its introduction into clinical practice in 1995 revealed secondary attack rates among susceptible children of 61%–100%.1–,3 This study by investigators from the Centers for Disease Control and Prevention and the Los Angeles County Department of Health Services, Calif, provides the first post-licensure, quantitative data on the secondary attack rates within households as well as an estimate of the effectiveness of varicella vaccine based on secondary attack rates in unvaccinated and vaccinated children and adolescents. For the study, active surveillance of varicella cases in a community of 320,000 within Los Angeles County was conducted; a total of 6,316 varicella cases were reported between 1997 and 2001. A varicella case was defined as “an illness characterized by acute onset of a diffuse papulovesicular rash without other known cause recognizing its variability in vaccinated persons.” Vaccination status of both cases and household contacts were based on immunization records and/or parental recall. Data from children and adolescents aged 1–14 years revealed secondary attack rates that varied according to age and by disease and vaccination status of the primary case and exposed household contacts. Among contacts aged 1–14 years exposed to unvaccinated cases, the secondary attack rate was 71.5% for unvaccinated household contacts and 15.1% among those who had been vaccinated. Overall, vaccinated cases were half as contagious as unvaccinated cases; however, vaccinated cases with 50 or more lesions were as contagious as unvaccinated cases. If fewer than 50 lesions were present in a vaccinated case, the secondary attack rate dropped to 23.4%. Calculated vaccine effectiveness for prevention of all disease was 78.9%, moderate disease 92%, and severe disease 100%. Disease (by history) was 90% protective in preventing a second episode of varicella. The reported variability of protection provided by the current varicella vaccine4 and the timing of its administration clearly require further study to provide the basis for decisions regarding the necessity of routine second varicella vaccination. 5 Meanwhile, pediatricians should reassure parents that although the varicella vaccine may not prevent the disease in every child, adverse reactions are uncommon, breakthrough disease is usually mild, and the prevention of severe disease almost certain. (See related articles in AAP Grand Rounds, May 2004;11:49–51.6–,8) Although varicella cases were based on clinical rather than laboratory criteria, the size of this study and consistency of the results suggest that the estimates of varicella vaccine efficacy and secondary attack rates are both valid and precise. You do not currently have access to this content.