Varicella Immunity and History of Infection

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Varicella Immunity and History of Infection

• Maryellen E. Gusic MD
• Assistant Professor of Pediatrics
• Penn State Childrens Hospital

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Introduction

• Immunization against varicella is recommended for
  susceptible, immunocompetant children over the
  age of 12 months.
• A reliable history of naturally occurring
  infection is considered to be evidence of
  immunity.

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Introduction continued

• Infection rarely occurs without the development
  of characteristic skin lesions.
• Parents are usually able to report a history of
  varicella infection in their child.

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Introduction continued

• Varicella immunity requires
• development of specific antibodies
• stimulation of cell mediated immunity
• Immune status of a child can be determined by
  measuring specific IgG immunoglobulin levels.

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Introduction continued

• Varicella in infants
• A modified specific antibody and cell mediated
  immune response has been described.
• mild infection
• effect of transplacentally acquired antibodies

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Introduction continued

• Natural infection is thought to provide life long
  immunity.
• Reinfections are observed in healthy children.
• inaccurate diagnoses?
• modified antibody and/or cell mediated immune
  response?

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Our Study

• Hypotheses
• Children infected with varicella early in life
  may have a modified immune response to infection
  and remain susceptible to reinfection.
• Children whose infection was clinically mild, may
  not have developed protective antibody titers and
  thus also remain susceptible to reinfection.

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Objectives

• To identify children with a history of natural
  infection whose illness occurred before 1 year of
  age
• To identify children whose infection would be
  classified as mild or moderate by determining the
  number of skin lesions present during the illness

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Objectives continued

• To determine if children with a history of
  natural infection before 1 year of age or with
  mild or moderate infection have protective
  antibody titers
• To determine if further questions to describe the
  skin lesions present aid in supporting the
  reliability of the history of infection

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Methods

• Children with a history of varicella infection
  identified by chart review and by parental
  questioning at clinic visits were included.
• Children with a known immunodeficiency were
  excluded.
• A varicella questionnaire was completed.

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Methods continued

• Varicella questionnaire
• patients current age
• age at which varicella infection occurred
• infection diagnosed by parent or health care
  professional
• description of illness
• vesicular, itchy, number of lesions

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Methods continued

• Finger stick blood samples were obtained for
  those children whose infection occurred before
  one year of age or who had less than 250 lesions
  during their infection.
• Serologic testing for anti-VZV IgG antibodies was
  performed by the National VZV Lab at the CDC.

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Methods continued

• Serologic testing
• ELISA assay for anti-VZV IgG antibodies
• Results recorded as mean adjusted OD reading and
  by objective rating
• 0.166 and above positive
• Equivocal results retested at lower serum dilution

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Methods continued

• Odds ratios were determined and a Chi square
  analysis was performed on the data.
• Research was approved by the Institutional Review
  Board of the Hershey Medical Center and the Penn
  State University College of Medicine.

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Results

• 32 patients were enrolled in the study
• 11 children had lt50 lesions
• 21 children had moderate infection
• 17 children were infected before 1 year of age
• 5 children whose infection occurred before 1 year
  of age had mild infection
• No child whose infection occurred before 1 year
  of age had gt250 lesions

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Results continued

• 30 patients underwent serologic testing
• 4 patients had negative antibody titers
• 6 patients had equivocal serologic results

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Conclusions

• Children with a history of mild varicella
  infection should be evaluated to determine if
  they have protective antibody titers.
• An immunocompetant child aged 12 months or older
  who has negative antibody titers should be
  immunized against varicella zoster virus.

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Conclusions continued

• Determining if the rash associated with the
  infection was itchy may further support the
  reliability of the diagnosis.
• Both parents and health care professionals may
  incorrectly identify an illness as varicella.

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Limitations of this Study

• Power of study limited by the small number of
  patients enrolled
• Results dependent upon parental reporting of age
  of infection, symptoms of disease
• Negative serologic titers may be result of
  inaccurate diagnoses

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Implications for Future Research

• Studies are needed to determine the factors that
  may interfere with the development of life long
  protective immunity to varicella infection.
• Further studies identifying the clinical signs
  and symptoms that ensure the accuracy of
  diagnosing varicella have important public health
  considerations.

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A Special Thanks to...

• Dr. Scott Schmid and the National VZV lab at the
  CDC
• Beth Anne Nagy, MS II, Penn State College of
  Medicine
• David Mauger, PhD, Department of Health
  Evaluation Sciences, Penn State College of
  Medicine