Prevention of Varicella: Recommendations by ACIP

Introduction

• Varicella (Chickenpox): Highly contagious disease caused by the varicella zoster virus (VZV).
• Secondary Attack Rates: Up to 90% among susceptible household contacts.
• Lifetime Immunity: Typically results post-infection.
• Herpes Zoster (Shingles): Reactivation of VZV causing a painful rash.

Epidemiology

• Transmission: Direct contact, droplet, aerosol from vesicular fluid or respiratory secretions.
• Incubation Period: 14-16 days (range: 10-21 days).
• Contagious Period: Begins 1-2 days before rash and ends when lesions crust.
• Annual Cases: Approx. 3.7 million in the U.S.
• Case Distribution: Most cases in children <15 years; rare in those >49 years.
• Hospitalizations: Common complications include bacterial infections, pneumonia, encephalitis.

Prenatal and Perinatal Exposure

• Risks: Congenital varicella syndrome with maternal infection during pregnancy.
• Effects: Can cause birth defects, zoster in infancy/childhood.

Nosocomial Transmission

• High-Risk Groups: Premature infants, immunocompromised patients, and patients receiving immunosuppressive therapy.
• Control Measures: Isolation, airflow control, serologic testing.

Varicella Antibody Testing

• History Reliability: Reliable in children but less so in adults.
• Serological Tests: Include CF, IFA, FAMA, ELISA among others.

Acyclovir

• Usage: Effective in reducing morbidity/mortality in immunocompromised patients.
• Recommendation: Not routine for healthy children, but for older adolescents and adults.

Live, Attenuated Varicella Virus Vaccine

• Oka Strain: Licensed for use in the U.S. in 1995 for healthy individuals 12 months and older.
• Immunogenicity: High seroconversion rates with persistent antibody titers.
• Efficacy: Reduced varicella incidence and severity.

Vaccine Recommendations

• Children <13 years: Single 0.5-mL dose recommended.
• Persons 13+ years: Two 0.5-mL doses, 4-8 weeks apart.
• High-Risk Groups: Health-care workers, family contacts of immunocompromised persons.

Adverse Events

• Common: Fever, injection site complaints, mild varicella-like rash.
• Serious Events: Encephalitis, ataxia, erythema multiforme reported but causality not established.

Contraindications and Precautions

• Allergies: History of anaphylactic reaction to any vaccine component.
• Illness: Postpone vaccination for severe illness.
• Altered Immunity: Vaccine not licensed for immunocompromised individuals.

VZIG for Postexposure Prophylaxis

• Max Benefit: Administer within 96 hours of exposure.
• Dosage: 125 U/10 kg body weight, max 625 U.
• Indications: For susceptible, immunocompromised persons after exposure.

Future Concerns

• Epidemiology Changes: Expected with increased vaccine use.
• Long-Term Immunity: Surveillance required to monitor antibody persistence.

Summary

• Emphasizes routine vaccination of children to prevent varicella and reduce complications.
• Special consideration for high-risk populations and situations.
• Ongoing surveillance needed to assess long-term impacts of vaccination and immunity.