What is the recommended treatment and prevention for chickenpox?

Treatment and Prevention of Chickenpox

Primary Treatment Approach

For immunocompetent patients, oral acyclovir should be initiated within 24 hours of rash onset at 20 mg/kg (maximum 800 mg) four times daily for 5 days, with treatment prioritized for adolescents ≥12 years, adults, secondary household contacts, and patients with chronic conditions, while immunocompromised patients require intravenous acyclovir 10 mg/kg every 8 hours for 7-10 days. 1, 2, 3

Specific Dosing by Patient Population

Children (<40 kg):

• Oral acyclovir 20 mg/kg per dose (maximum 800 mg) four times daily for 5 days 1, 2, 3
• Treatment must begin within 24 hours of rash onset for maximum efficacy 1, 4

Adolescents ≥12 years and Children >40 kg:

• Oral acyclovir 800 mg four times daily for 5 days 1, 2, 3

Adults:

• Oral acyclovir 800 mg four times daily for 5-7 days 1, 3
• Adults have more severe disease and higher complication rates than children 5, 6

Immunocompromised Patients:

• Intravenous acyclovir 10 mg/kg every 8 hours for 7-10 days is mandatory 1, 2, 5
• Alternative dosing: 500 mg/m² IV every 8 hours in children >1 year 1
• Continue until no new lesions appear for 48 hours 1

High-Risk Groups Requiring Antiviral Treatment

The following patients should receive acyclovir therapy even if otherwise immunocompetent:

• Adolescents ≥12 years and all adults 1, 2, 5
• Patients with chronic cutaneous or pulmonary disorders 1, 2
• Patients receiving long-term salicylate therapy 1, 2
• Patients on corticosteroid therapy (short, intermittent, or aerosolized) 1, 2
• Secondary household contacts of infected children 1
• Pregnant women (though routine use not generally recommended; Category B) 1

Critical Timing Considerations

The 24-hour window from rash onset is the most critical factor determining treatment efficacy. 1, 4 A controlled trial demonstrated a clear gradient in clinical response correlating with time from rash onset to treatment initiation 4. Patients treated on day 1 had significantly shortened event times compared to those starting on day 2 or 3, including faster time to maximum lesion formation, 50% healing, and resolution of facial lesions 4.

Treatment initiated >24 hours after rash onset still provides some benefit, particularly in adolescents and adults, but efficacy is reduced 4, 5. There are no data on treatment initiated >72 hours after onset for herpes zoster 3.

Duration of Therapy

Five days of oral acyclovir is sufficient for immunocompetent patients, as a 7-day course provides no additional benefit. 1, 4 The controlled trial by Dunkle et al. demonstrated equivalent outcomes between 5-day and 7-day regimens 4.

Immunocompromised patients require 7-10 days of IV therapy 1, 2.

Post-Exposure Prophylaxis

For Immunocompromised Patients

Varicella zoster immune globulin (VZIG) should be administered as soon as possible, ideally within 96 hours but up to 10 days after exposure. 7, 1, 2

If VZIG is unavailable:

• Oral acyclovir 10 mg/kg four times daily for 7 days, starting 7-10 days after exposure 7, 1, 2

For Pregnant Women and Neonates

• Pregnant women without evidence of immunity should receive VZIG 1, 2
• Neonates born to mothers with varicella 5 days before to 2 days after delivery should receive VZIG 1, 2
• Premature infants <28 weeks gestation or <1,000 g regardless of maternal immunity should receive VZIG 1, 2

Post-Exposure Vaccination

Varicella vaccine administered within 3-5 days of exposure may prevent illness or modify disease severity. 7 If exposure does not cause infection, post-exposure vaccination provides protection against subsequent exposures 7. This approach is recommended for susceptible persons and has been used successfully for outbreak control 7.

Prevention Through Vaccination

Routine Vaccination Recommendations

All states should require children entering child care facilities and elementary schools to have received varicella vaccine or have other evidence of immunity (physician-diagnosed disease, reliable history, or serologic evidence). 7

States should consider implementing vaccination requirements for children entering middle school to prevent susceptible individuals from reaching adulthood without immunity 7.

High-Risk Groups for Vaccination Priority

Vaccination is strongly recommended for susceptible persons ≥13 years at high risk for exposure or transmission, including:

• Healthcare workers (birth before 1980 is NOT considered evidence of immunity for HCP) 7
• Adolescents and adults living in households with children 7
• Susceptible household contacts of immunocompromised patients to prevent transmission 1, 2

Healthcare Worker Management

Healthcare workers must have documented evidence of immunity; serologic screening before vaccination is cost-effective for those with negative or uncertain history. 7

After exposure to VZV:

• HCP with 2 vaccine doses: monitor daily on days 10-21 for fever, skin lesions, and symptoms; place on sick leave immediately if symptoms develop 7
• HCP with 1 vaccine dose: administer second dose within 3-5 days after exposure (if ≥4 weeks since first dose) 7
• Unvaccinated HCP without immunity: furlough from days 10-21 after exposure; administer post-exposure vaccination as soon as possible 7, 2

Vaccination Timing After VZIG

Delay varicella vaccination 5 months after VZIG administration 1, 2

Infection Control Measures

Isolate patients until all lesions have crusted over. 1, 2 Chickenpox is highly contagious and can spread through airborne transmission, with documented cases of transmission without direct contact with the index patient 7.

Important Clinical Caveats and Pitfalls

Antibody Testing Limitations

Do not rely on antibody titers in patients with nephrotic-range proteinuria or those receiving IVIG infusions, as they are unreliable. 7, 2 Diagnosis should rely on clinical features with or without PCR detection of virus from vesicle samples 7.

Commercial serologic assays may not be sensitive enough to detect antibody after vaccination in all instances 7. Latex agglutination (LA) tests are generally more sensitive than commercial ELISAs for detecting antibody after natural infection 7.

Vaccination Contraindications

Live varicella vaccine is absolutely contraindicated in immunocompromised patients due to risk of disseminated infection. 1, 2 For patients on immunomodulators unable to receive live vaccination, advise seeking post-exposure prophylaxis if exposed to active chickenpox or herpes zoster 1.

Acyclovir Limitations

Acyclovir does not eradicate latent virus or affect subsequent risk, frequency, or severity of herpes zoster recurrences 1. Antibody titers after infection in children receiving acyclovir do not differ substantially from untreated patients 1.

Renal Impairment Considerations

Dosage adjustment is mandatory in patients with renal impairment. 3 For creatinine clearance 0-10 mL/min/1.73 m², reduce 800 mg every 4 hours to 800 mg every 12 hours 3. Patients on hemodialysis require an additional dose after each dialysis session 3.

Caution is required when administering acyclovir with potentially nephrotoxic agents, as this increases risk of renal dysfunction and reversible CNS symptoms 3. Adequate hydration should be maintained 3.

Pregnancy and Nursing

Acyclovir is Pregnancy Category B 1, 3. A prospective registry of 749 pregnancies with first-trimester acyclovir exposure showed birth defect rates approximating the general population, though the registry size was insufficient for definitive conclusions 3.

Acyclovir concentrations in breast milk range from 0.6 to 4.1 times corresponding plasma levels, potentially exposing nursing infants to acyclovir 3.