Varicella Vaccine attenuated

Usage

• Varicella vaccine is prescribed for the prevention of chickenpox (varicella), a highly contagious disease caused by the varicella-zoster virus (VZV). It is also effective in preventing herpes zoster (shingles), a painful reactivation of VZV later in life.
• Pharmacological Classification: Vaccine (Live attenuated viral vaccine).
• Mechanism of Action: The vaccine contains a weakened, live form of the varicella-zoster virus. Upon administration, the virus replicates, triggering an immune response without causing the full-blown disease. This generates immunological memory, protecting against future VZV infections.

Alternate Names

• Varicella vaccine live
• Chickenpox vaccine
• Brand Names:
  • Varivax®
  • ProQuad® (combined MMRV vaccine)

How It Works

• Pharmacodynamics: The vaccine mimics a natural varicella infection but on a much smaller scale. The attenuated virus replicates within the body, stimulating both humoral (antibody-mediated) and cell-mediated immunity. This leads to the production of antibodies and specific T-cells that can neutralize VZV upon subsequent exposure.

• Pharmacokinetics:

  • Absorption: The vaccine is administered subcutaneously, where it is gradually absorbed into the bloodstream.
  • Metabolism: The virus replicates within the body, primarily in the lymphatic system. The immune system eliminates the attenuated virus over time.
  • Excretion: Viral particles and their components are eliminated through multiple routes, including urine and feces.

• Mode of Action: The vaccine triggers the adaptive immune response. Antigen-presenting cells process viral antigens and present them to lymphocytes, leading to activation of B cells and T cells specific for VZV. Activated B cells differentiate into plasma cells, producing antibodies that neutralize the virus. Cytotoxic T lymphocytes are also activated, contributing to the elimination of infected cells.

• Receptor Binding/Enzyme Inhibition: The vaccine’s mechanism primarily involves activating the adaptive immune response, rather than direct receptor binding or enzyme inhibition. It relies on activating the immune system to produce antibodies and cytotoxic T cells to counteract the varicella virus.

• Elimination Pathways: The attenuated virus and viral components are eliminated through multiple pathways including the lymphatic system and via renal and hepatic routes.

Dosage

Standard Dosage

Adults (≥13 years):

• 0.5 ml subcutaneously administered as two doses, 4 to 8 weeks apart. ProQuad® (MMRV) is not approved for this age group.

Children (12 months - 12 years):

• 0.5 ml subcutaneously administered as two doses, separated by at least 3 months.
• MMRV (ProQuad®) is approved for this age group and may be preferred for the second dose (15 months-12 years) and first dose at ≥48 months.
• For the first dose (12–47 months), MMR and varicella vaccines are generally given separately unless the parent or caregiver prefers MMRV.

Special Cases:

• Elderly Patients: Standard adult dosage.
• Patients with Renal Impairment: No dose adjustment is typically necessary.
• Patients with Hepatic Dysfunction: No dose adjustment is typically necessary.
• Patients with Comorbid Conditions: Use with caution in immunocompromised individuals. Consult specialist advice if needed.

Clinical Use Cases

Varicella vaccine is primarily used for prevention, not treatment, hence its use in the following scenarios is not applicable:

• Intubation: Not applicable.
• Surgical Procedures: Not applicable.
• Mechanical Ventilation: Not applicable.
• Intensive Care Unit (ICU) Use: Not applicable.
• Emergency Situations: Not applicable.

Dosage Adjustments

• Immunosuppressed individuals: Varicella vaccine is generally contraindicated for individuals with severe immunodeficiency.

Side Effects

Common Side Effects:

• Pain, redness, or swelling at the injection site.
• Mild fever.
• A small number of individuals (around 5%) may develop a mild, localized varicella-like rash 5-26 days post-vaccination.

Rare but Serious Side Effects:

• Severe allergic reaction (anaphylaxis).
• Pneumonia.
• Encephalitis.

Long-Term Effects:

• Herpes zoster (shingles) may still occur, though at a reduced incidence and severity compared to unvaccinated individuals.

Adverse Drug Reactions (ADR):

• Thrombocytopenia (low platelet count).
• Disseminated varicella (rare in healthy individuals, primarily seen in immunocompromised).

Contraindications

• Pregnancy.
• Severe immunodeficiency (e.g., leukemia, lymphoma, congenital immunodeficiency).
• Active, untreated tuberculosis.
• Current moderate or severe illness with or without fever.
• Allergy to any component of the vaccine, including gelatin or neomycin.

Drug Interactions

• Immunosuppressants: Avoid concurrent administration.
• Salicylates: Should be avoided for 6 weeks after vaccination due to a theoretical increased risk of Reye’s syndrome.
• Recent blood transfusion: Postpone vaccination for at least 3 months.

Pregnancy and Breastfeeding

• Pregnancy Safety Category: Contraindicated.
• Fetal Risks: Potential risk of congenital varicella syndrome if infected with wild-type VZV during pregnancy. However, the vaccine itself is contraindicated.
• Breastfeeding: Caution advised. Limited data are available.

Drug Profile Summary

• Mechanism of Action: Live attenuated viral vaccine stimulating immune response to VZV.
• Side Effects: Injection site reactions, fever, mild rash, rarely serious complications.
• Contraindications: Pregnancy, immunodeficiency, active tuberculosis.
• Drug Interactions: Immunosuppressants, salicylates.
• Pregnancy & Breastfeeding: Contraindicated in pregnancy.
• Dosage: 0.5ml SC x 2 doses; 3 months apart for children, 4-8 weeks apart for adults.

Popular Combinations

• MMRV (Measles, Mumps, Rubella, and Varicella) combined vaccine.

Precautions

• General Precautions: Assess immune status. Postpone vaccination in individuals with moderate or severe illness. Monitor for allergic reactions.
• Specific Populations: Standard precautions as mentioned above.
• Lifestyle Considerations: No specific lifestyle considerations.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Varicella Vaccine attenuated?

A: Children (12 months-12 years): 0.5 ml subcutaneously, two doses, 3 months apart. Adults (≥13 years): 0.5 ml subcutaneously, two doses, 4-8 weeks apart.

Q2: Can pregnant women receive the varicella vaccine?

A: No, the varicella vaccine is contraindicated in pregnancy.

Q3: What are the common side effects of the varicella vaccine?

A: Common side effects include pain, redness, swelling at the injection site, mild fever, and possibly a mild localized rash.

Q4: How effective is the varicella vaccine?

A: Two doses of the vaccine are approximately 98% effective in preventing any form of varicella and almost 100% effective against severe disease.

Q5: Can the varicella vaccine be given to immunocompromised individuals?

A: Generally no. The vaccine is contraindicated in individuals with severe immunodeficiency. Consult a specialist for specific guidance.

Q6: What is the interval between doses for the varicella vaccine?

A: For children (12 months-12 years), the interval is at least 3 months. For adults (≥13 years), it’s 4-8 weeks.

Q7: Can the varicella vaccine be given with other vaccines?

A: Yes, it can be administered concurrently with other vaccines.

Q8: What should be done if a dose of varicella vaccine is missed?

A: Administer the missed dose as soon as possible. There’s no need to restart the series.

Q9: Does the varicella vaccine completely eliminate the risk of shingles?

A: No, it reduces the risk of shingles and its severity but does not eliminate it completely.