Pathogenesis And Epidemiology
Organism Profile
- Gram-positive, catalase-negative, facultatively anaerobic diplococci.
- Polysaccharide capsule dictates virulence and type-specific identification.
- Transmitted primarily via respiratory droplets.
Disease Burden
- Infants and young children act as main reservoirs.
- Nasopharyngeal carriage ranges from 27% to 85% globally.
- Causes invasive pneumococcal disease including meningitis, bacteremia, and severe pneumonia.
- Causes non-invasive disease including acute otitis media and sinusitis.
- Highly prevalent serotypes in India include 1, 6B, 14, 19F, and 23F.
Antimicrobial Resistance
- Macrolide resistance exceeds 70% in Asian isolates.
- Penicillin and multidrug resistance frequently associated with serotypes 6B, 23F, 14, 9V, 18A, 18F, and 19A.
Vaccine Classifications
Pneumococcal Polysaccharide Vaccine (PPSV23)
- Unconjugated vaccine containing 25 µg capsular polysaccharide from 23 serotypes.
- Elicits T-cell-independent B cell immune response.
- Poorly immunogenic in children below 2 years of age.
- Fails to induce immunologic memory.
- Does not reduce nasopharyngeal carriage.
- Cannot provide herd immunity.
- Dosage: 0.5 mL, intramuscular or subcutaneous.
- Administration site: Deltoid muscle.
- Storage requirement: 2–8°C, do not freeze.
Pneumococcal Conjugate Vaccines (PCVs)
- Capsular polysaccharides conjugated to specific carrier proteins.
- Elicits T-cell-dependent immune activation.
- Highly immunogenic during infancy.
- Induces robust immunologic memory.
- Reduces nasopharyngeal bacterial carriage by almost 50%.
- Generates significant herd effect.
Immunization Schedule And Dosage
Routine Immunization Guidelines
| Organization | Primary Series | Booster Dose | Route & Site |
|---|
| Universal Immunization Programme (UIP) | Two doses at 6 and 14 weeks | Single booster at 9–12 months | 0.5 mL Intramuscular, Anterolateral thigh |
| Indian Academy of Pediatrics (IAP) | Three doses at 6, 10, 14 weeks | Single booster at 15–18 months | 0.5 mL Intramuscular, Anterolateral thigh |
Catch-Up Vaccination Guidelines
| Age At First Dose | PCV-10/PCV-13 Primary Series | PCV-10/PCV-13 Booster Dose |
|---|
| 7–11 months | Two doses 4 weeks apart | Single dose during 2nd year (minimum 8 weeks later) |
| 12–23 months | Two doses 8 weeks apart | Not applicable |
| 24–59 months | PCV-13: One dose. PCV-10: Two doses 8 weeks apart | Not applicable |
| ≥60 months | Routine administration not recommended for healthy children | Not applicable |
High-Risk Populations
Identification Of High-Risk Groups
- Chronic heart disease including cyanotic congenital heart disease and cardiac failure.
- Chronic lung disease including asthma requiring prolonged high-dose oral corticosteroids.
- Diabetes mellitus.
- Cerebrospinal fluid leaks.
- Cochlear implants.
- Primary immunodeficiency, human immunodeficiency virus infection, immunosuppressive therapy.
- Anatomic or functional asplenia, sickle cell disease.
- Prematurity and very low birth weight.
Vaccination Strategy For High-Risk Children
- Conjugate vaccines preferred over polysaccharide vaccines due to herd protection potential and superior immunogenicity.
- PPSV23 strictly contraindicated below 2 years of age.
| Age & Prior Vaccination | PCV-13 Recommendation | PPSV23 Recommendation |
|---|
| <23 months (Nil prior doses) | Age-appropriate routine recommendations | Not recommended |
| 24–71 months (4 prior doses PCV-13) | None | Dose 1: 8 weeks after last PCV-13. Dose 2: 5 years after Dose 1 |
| 24–71 months (<3 prior doses PCV-13) | Two doses 8 weeks apart | Dose 1: 8 weeks after last PCV-13. Dose 2: 5 years after Dose 1 |
| 6–18 years (Nil prior doses) | One dose PCV-13 | Dose 1: 8 weeks after PCV-13. Dose 2: 5 years after Dose 1 |
- Maximum two doses of PPSV23 recommended per lifetime.
- If cochlear implant placement planned, complete PCV-13 and PPSV23 vaccination 2 weeks prior to surgery.
Efficacy And Safety Profile
Clinical Effectiveness
- Invasive pneumococcal disease: Pooled vaccine efficacy of 80% against vaccine-type disease.
- Radiologically defined pneumonia: Pooled vaccine efficacy of 27%.
- Acute otitis media: Relative risk reduction up to 53% for pneumococcal otitis media.
- Effectiveness of one PCV-13 dose estimated at 48%, two doses at 87%, and three doses (2+1 schedule) at 100%.
Adverse Events Following Immunization
- Common events: Mild to moderate injection-site reactions (pain, redness, swelling), fever, irritability, decreased appetite, altered sleep patterns (10% of vaccinees).
- Uncommon events: Fever >39°C (1% to 10%), vomiting, diarrhea (0.1% to 1%).
- Rare events: Hypersensitivity reactions, convulsions, hypotonic-hyporesponsive episodes (<0.1%).
