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    Background Paper on Varicella Vaccine

    SAGE Working Group on Varicella and Herpes Zoster Vaccines

    Contents Introduction ................................................................................................................................................................2

    Objectives ...................................................................................................................................................................2

    Methods .....................................................................................................................................................................3

    Results ........................................................................................................................................................................4

    Pathogen and transmission ....................................................................................................................................4

    Clinical description of varicella ...............................................................................................................................4

    Varicella epidemiology ...........................................................................................................................................5

    Methodological issues ........................................................................................................................................5

    Incidence ............................................................................................................................................................5

    Severe disease burden .......................................................................................................................................7

    Risk factors for severe disease ...........................................................................................................................8

    Epidemiology of varicella in the vaccine era ......................................................................................................9

    Varicella vaccines................................................................................................................................................. 12

    Measure of vaccine protection........................................................................................................................ 12

    Pre-licensure vaccine efficacy ..................................................................................................................... 13

    Post-licensure vaccine effectiveness ........................................................................................................... 13

    One dose vaccine effectiveness .............................................................................................................. 13

    Two dose vaccine effectiveness .............................................................................................................. 15

    Duration of vaccine protection ........................................................................................................................ 20

    Vaccine safety .................................................................................................................................................. 24

    Monovalent varicella vaccine ...................................................................................................................... 24

    MMRV .......................................................................................................................................................... 25

    Transmission of vaccine virus ...................................................................................................................... 26

    Herpes zoster after vaccination ................................................................................................................... 26

    Co-administration of monovalent varicella vaccine and MMRV with other childhood vaccines ................... 31

    Modeling the potential impact of a childhood varicella vaccination program on varicella and adult herpes

    zoster epidemiology ............................................................................................................................................ 31

    Potential for shift in the age at infection and increase burden of varicella .................................................... 31

    Potential impact on adult herpes zoster epidemiology .................................................................................. 32

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    Cost effectiveness of varicella vaccination .......................................................................................................... 34

    Immunocompromised populations ..................................................................................................................... 34

    Varicella in immunocompromised populations .............................................................................................. 34

    Varicella vaccine in imunocompromised populations..................................................................................... 35

    Varicella in healthcare settings ........................................................................................................................... 39

    Conclusions and recommendations ........................................................................................................................ 39

    High priority research questions ............................................................................................................................. 43

    References ............................................................................................................................................................... 44

    Introduction Varicella or chickenpox is an acute, highly contagious viral disease with worldwide distribution. It is

    characterized by a generalized, pruritic maculopapular vesicular rash that appears in successive crops and that rapidly progresses to develop crusts and scabs 1. Although varicella is usually a self-limited illness of childhood, it can cause significant morbidity and mortality in otherwise healthy children and adults and may assume greater relative importance in preventable disease burden as other diseases are prevented through vaccination. Morbidity and mortality are higher in immunocompetent infants and adults as well as in immunocompromised persons compared to healthy children1. Nonetheless, due the ubiquitous nature of varicella infection, the majority of severe disease burden occurs in healthy persons, primarily children2, 3. Varicella is the manifestation of the primary infection caused by the varicella-zoster virus (VZV). Following the primary infection, the virus remains latent in neural and intestinal ganglia and may reactivate years or decades later to cause herpes zoster (HZ) or shingles4. HZ develops primarily in healthy adults after the age of 50 and in immunocompromised persons of all ages. In its full clinical expression, HZ causes pain which is followed by a pruritic vesicular rash usually restricted to one or more dermatomes that closely overlap the segmental distribution of the nerve cells in which latent VZV resided4. Rash can disseminate beyond the initial dermatome in immunocompromised patients.

    Varicella can be treated with antiviral drugs5. However, considering the minimal clinical benefit in healthy persons and the cost of the treatment, antiviral treatment is recommended for persons at high risk for severe varicella. Varicella-zoster immune globulins are effective as post-exposure prophylaxis to reduce disease severity in persons at high risk for severe varicella but they are also costly and not widely available worldwide5. Control of varicella can be achieved only by vaccination. A varicella vaccine based on attenuated live VZV virus (Oka strain) was developed approximately four decades ago and some countries started introducing vaccination into the childhood immunization programs after more widespread global licensure that followed licensure in the United States in 1995. Currently there are several formulations of live attenuated varicella vaccines. While these vaccines are licensed and available throughout the world they are recommended for routine use only in a small number of countries, primarily industrialized countries (i.e., Unites States, Canada, Australia, Germany, Greece, Latvia, Israel, Uruguay, Costa Rica, United Arab Emirates, Saudi Arabia, Quatar, Taiwan, various regions in Spain and Italy). Where high coverage rates have been attained, vaccination has resulted in important declines in varicella-related incidence, morbidity and mortality6-9.

    Objectives The SAGE Working group on varicella and herpes zoster vaccines (established in May 2012) was tasked with

    reviewing the evidence, identifying information gaps, and guiding the work to formulate proposed

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    recommendations related to the use of varicella vaccine to update the 1998 varicella vaccine WHO position paper for SAGE review. This report reviews the evidence related to the main topics considered by the working group, including:

    1. Varicella epidemiology: the global incidence and burden of disease caused by varicella according to country development status

    2. Safety and effectiveness profile of varicella vaccine and duration of protection following i

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