Varicella, commonly known as chickenpox, is a highly contagious disease caused by the varicella-zoster virus (VZV). Transmission typically occurs through respiratory droplets or direct contact with vesicular fluid. Given its significant morbidity in susceptible individuals, especially immunocompromised patients, neonates, and non-immune pregnant women, timely post-exposure interventions are essential. This article outlines the most effective strategies for the prevention of varicella after exposure, grounded in clinical evidence and public health policy.
Understanding Varicella-Zoster Virus and Its Transmission
The varicella-zoster virus has an incubation period of 10 to 21 days, with most cases developing symptoms around day 14 to 16 post-exposure. Individuals are infectious from 1 to 2 days before the appearance of rash until all lesions have crusted.
Transmission Modalities:
- Airborne spread via respiratory droplets
- Direct contact with vesicular fluid
- Indirect contact via contaminated surfaces (less common)
Assessing Exposure Risk and Susceptibility
Definition of Significant Exposure
A person is considered significantly exposed if they:
- Share indoor airspace for over an hour with an infectious individual
- Have face-to-face interaction
- Have direct contact with infectious vesicular fluid
Identifying High-Risk Groups
Post-exposure prophylaxis (PEP) is crucial for the following populations:
- Immunocompromised individuals
- Pregnant women without immunity
- Newborns exposed perinatally
- Healthcare workers with unknown varicella status
- Non-immune household contacts
Varicella Vaccination as Primary Prevention Post-Exposure
Timely Vaccination for Eligible Individuals
Administering the varicella vaccine within 3 to 5 days after exposure can prevent or significantly attenuate the disease.
Vaccination Criteria:
- Individuals ≥12 months old
- Not previously vaccinated or infected
- Not pregnant or immunocompromised
Effectiveness of Post-Exposure Vaccination
- If given within 3 days: Up to 90% effectiveness in preventing clinical varicella
- Within 5 days: Reduced disease severity even if infection occurs
Varicella-Zoster Immune Globulin (VZIG) for High-Risk Populations
VZIG Indications
Varicella-Zoster Immune Globulin is administered intramuscularly within 10 days of exposure to high-risk individuals unable to receive the vaccine:
- Immunocompromised patients
- Neonates whose mothers show symptoms 5 days before to 2 days after delivery
- Non-immune pregnant women
- Premature infants (≥28 weeks if mothers are non-immune; <28 weeks regardless of maternal status)
Administration and Dosage
- Given IM, based on weight (125 IU per 10 kg, max 625 IU)
- Must be administered promptly to ensure effectiveness
Antiviral Therapy: Acyclovir and Alternatives
Oral Acyclovir as Post-Exposure Prophylaxis
In individuals not eligible for VZIG or vaccination, acyclovir is an effective alternative when administered 7 to 10 days post-exposure.
Dosage Guidelines:
- Children: 20 mg/kg/dose, four times daily for 5–7 days
- Adults: 800 mg, five times daily for 5–7 days
When to Use Antivirals
- Immunocompetent children and adults with moderate exposure
- Late presenters beyond VZIG window
- Breakthrough cases in vaccinated individuals
Isolation and Infection Control Measures
Preventing Secondary Transmission
- Infected individuals must remain isolated until lesions have fully crusted
- Exposed non-immune persons should avoid contact with high-risk individuals from day 8 to 21 post-exposure
- Healthcare institutions must implement airborne and contact precautions
Public Health Implications and Herd Immunity
Importance of Immunization Programs
Widespread varicella vaccination reduces community transmission, thereby protecting vulnerable groups indirectly through herd immunity. The two-dose varicella vaccine schedule ensures high seroconversion rates and long-term immunity.
Coverage Targets:
- ≥90% among children under 5
- Catch-up programs for adolescents and adults without immunity
Surveillance and Follow-Up
- Monitor all exposed individuals for 21 days
- Educate families and caregivers about signs of varicella
- Document prophylaxis interventions for future immunization planning
Effective prevention of varicella after exposure requires a time-sensitive and risk-based approach. Immediate vaccination, administration of VZIG in high-risk populations, judicious use of antiviral agents, and strict isolation measures form the backbone of post-exposure prophylaxis. Through proactive management and comprehensive public health policies, the transmission of varicella-zoster virus can be significantly curtailed, safeguarding at-risk individuals and reducing disease burden.
