Varicella Vaccines
Introduction to Varicella Vaccines
Varicella vaccines are immunizations designed to protect against varicella-zoster virus (VZV), which causes chickenpox and shingles. Developed in the 1970s and widely implemented since the 1990s, these vaccines have significantly reduced the incidence and severity of varicella infections worldwide.
Key points:
- First developed by Dr. Michiaki Takahashi in Japan in 1974
- Licensed for use in the United States in 1995
- Contain live attenuated VZV derived from the Oka strain
- Available as monovalent vaccines or in combination with measles, mumps, and rubella (MMRV)
- Recommended as part of routine childhood immunization in many countries
Varicella-Zoster Virus and Disease
Understanding the pathogen and its associated diseases is crucial for appreciating the importance of varicella vaccination.
Varicella-Zoster Virus (VZV)
- Alphaherpesvirinae subfamily of herpesviruses
- Double-stranded DNA virus
- Highly contagious through respiratory droplets and direct contact with lesions
Chickenpox (Primary VZV Infection)
- Typically occurs in childhood
- Characterized by vesicular rash, fever, and malaise
- Usually self-limiting but can lead to complications
Herpes Zoster (Shingles)
- Results from reactivation of latent VZV in sensory ganglia
- Typically occurs in older adults or immunocompromised individuals
- Presents as a painful, unilateral vesicular rash in a dermatomal distribution
Types of Varicella Vaccines
There are several formulations of varicella vaccines available globally:
1. Monovalent Varicella Vaccine
- Contains only the live attenuated VZV Oka strain
- Examples: Varivax (Merck), Varilrix (GlaxoSmithKline)
- Used for primary immunization and booster doses
2. Combination MMRV Vaccine
- Combines measles, mumps, rubella, and varicella vaccines
- Examples: ProQuad (Merck), Priorix-Tetra (GlaxoSmithKline)
- Typically used for children aged 12 months to 12 years
3. Zoster Vaccine
- Higher potency than chickenpox vaccines
- Used to prevent shingles in older adults
- Examples: Zostavax (live attenuated, being phased out), Shingrix (recombinant, preferred)
Efficacy and Safety of Varicella Vaccines
Efficacy
- Single dose: 80-85% effective in preventing varicella infection
- Two-dose regimen: 98% effective in preventing severe disease
- Breakthrough infections are usually milder
Safety Profile
- Generally well-tolerated
- Common side effects: injection site reactions, low-grade fever
- Rare adverse events: febrile seizures (slightly increased risk with MMRV)
Long-term Effectiveness
Studies have shown persistent antibody levels and protection for at least 10-20 years post-vaccination. Ongoing surveillance continues to monitor long-term effectiveness and the potential need for booster doses in adulthood.
Varicella Vaccination Schedule
The recommended schedule varies by country, but generally follows these guidelines:
United States (CDC recommendations)
- First dose: 12-15 months of age
- Second dose: 4-6 years of age
- Catch-up vaccination for older children and adults without evidence of immunity
Alternative Schedules
- Some countries implement a single-dose schedule
- Two doses may be given 3 months apart for children 12 months to 12 years
- Adults and adolescents: two doses 4-8 weeks apart
Combination with Other Vaccines
Varicella vaccine can be administered concurrently with other vaccines, using separate syringes and injection sites.
Contraindications and Precautions
Contraindications
- Severe allergic reaction to a previous dose or vaccine component
- Pregnancy
- Severe immunodeficiency (e.g., advanced HIV, chemotherapy)
Precautions
- Moderate or severe acute illness
- Recent blood product administration
- Tuberculosis
- Family history of congenital or hereditary immunodeficiency
Special Considerations
Patients with a history of thrombocytopenia or thrombocytopenic purpura should be carefully evaluated before vaccination. The risks and benefits should be weighed for individuals with HIV infection and CD4+ T-lymphocyte counts ≥200 cells/μL.
Varicella Vaccination in Special Populations
Healthcare Workers
- Recommended for all healthcare personnel without evidence of immunity
- Important for preventing nosocomial transmission
Immunocompromised Individuals
- Generally contraindicated for severe immunodeficiency
- May be considered for mild immunosuppression under specialist guidance
- Household contacts of immunocompromised persons should be vaccinated
Pregnant Women
- Contraindicated during pregnancy
- Women should avoid pregnancy for 1 month after vaccination
- Inadvertent vaccination during pregnancy is not an indication for termination
International Travelers
Vaccination should be considered for susceptible individuals traveling to areas with high varicella prevalence.
Post-Exposure Prophylaxis
Varicella vaccine can be used for post-exposure prophylaxis in certain situations:
- Most effective when given within 3 days of exposure, but may be given up to 5 days post-exposure
- Can prevent or modify the course of infection in exposed, susceptible individuals
- Alternative: Varicella-zoster immune globulin (VZIG) for high-risk individuals who cannot receive the vaccine
Indications for Post-Exposure Vaccination
- Unvaccinated, immunocompetent individuals ≥12 months of age
- Healthcare workers without evidence of immunity
- Pregnant women may be candidates for VZIG
Global Impact of Varicella Vaccination
The implementation of varicella vaccination programs has had significant public health benefits:
- Dramatic reduction in varicella incidence, hospitalizations, and deaths
- Decreased economic burden due to reduced healthcare costs and work absenteeism
- Indirect protection of unvaccinated individuals through herd immunity
Challenges and Considerations
- Potential for age shift in disease burden to older individuals
- Impact on herpes zoster epidemiology (ongoing research)
- Vaccine hesitancy and misinformation
- Global disparities in vaccine access and implementation
Continued surveillance and research are essential to optimize vaccination strategies and address emerging challenges in varicella prevention.
Varicella Vaccines
- What disease does the varicella vaccine prevent?
Chickenpox - What causes chickenpox?
Varicella-zoster virus (VZV) - At what age is the first dose of varicella vaccine typically given?
12-15 months - When is the second dose of varicella vaccine typically given?
4-6 years - How many doses of varicella vaccine are required for full protection?
Two doses - What is the minimum interval between the two doses of varicella vaccine?
3 months for children under 13, 4 weeks for those 13 and older - Can adults get the varicella vaccine?
Yes, if they've never had chickenpox or been vaccinated - What is the efficacy of the varicella vaccine after two doses?
Over 90% effective in preventing any varicella infection, nearly 100% effective in preventing severe cases - Can pregnant women receive the varicella vaccine?
No, it's contraindicated during pregnancy - What are common side effects of the varicella vaccine?
Soreness at injection site, fever, mild rash - Is the varicella vaccine a live vaccine?
Yes, it contains live attenuated virus - Can the varicella vaccine be given with other vaccines?
Yes, it can be administered with other vaccines - Can someone who has had chickenpox get the vaccine?
It's not necessary, as they've developed natural immunity - Is there a combination vaccine that includes varicella?
Yes, the MMRV vaccine combines measles, mumps, rubella, and varicella - Can the varicella vaccine cause chickenpox?
In rare cases, it can cause a mild, chickenpox-like rash - Who should not receive the varicella vaccine?
Pregnant women, people with severe immunodeficiency, and those allergic to vaccine components - Can the varicella vaccine prevent shingles?
It may reduce the risk of shingles later in life - What is the storage temperature for varicella vaccines?
-50°C to -15°C (-58°F to 5°F) - Can the varicella vaccine be given after exposure to chickenpox?
Yes, if given within 3-5 days of exposure, it may prevent or lessen the severity of the disease - Is the varicella vaccine part of the routine childhood immunization schedule in all countries?
No, it varies by country based on disease burden and economic considerations - Can immunocompromised individuals receive the varicella vaccine?
Generally no, but it depends on the level of immunosuppression - What organization recommends varicella vaccination globally?
The World Health Organization (WHO) - In which year was the varicella vaccine first licensed?
1995 in the United States - How long does immunity from the varicella vaccine last?
Studies suggest protection lasts for at least 10-20 years - Can adults who received only one dose as children get a second dose?
Yes, it's recommended for those who received only one dose - Is there a separate varicella vaccine for adults and children?
No, the same vaccine is used for all age groups - Can the varicella vaccine reactivate later as shingles?
It's possible but much less likely than with natural infection - What percentage of people develop protective antibodies after two doses of varicella vaccine?
Over 98% - Is there a need for booster doses after completing the initial varicella vaccine series?
Currently, no booster doses are recommended after the two-dose series - Can the varicella vaccine be given to breastfeeding mothers?
Yes, it's safe for breastfeeding mothers
