Key Differences Between PCV and PPSV Vaccines
The fundamental difference is that pneumococcal conjugate vaccines (PCV) induce T-cell dependent immune responses with memory B-cell formation, providing stronger and longer-lasting protection, while pneumococcal polysaccharide vaccines (PPSV) induce T-cell independent responses without immunologic memory, resulting in shorter duration of protection. 1
Immunologic Mechanism
PCV (Conjugate Vaccines)
- Polysaccharides are chemically conjugated to a carrier protein (CRM197), which activates T-helper cells and creates memory B-cells 1
- This T-cell dependent response generates both stronger primary responses and robust booster responses upon re-vaccination 2, 3
- PCV induces significantly higher functional antibody activity (measured by opsonophagocytic killing) compared to PPSV23 for the majority of shared serotypes 3, 4
PPSV23 (Polysaccharide Vaccine)
- Contains free polysaccharide antigens without protein conjugation 5
- Induces T-cell independent immune responses that do not create memory B-cells, leading to potentially shorter protection duration 1
- Re-vaccination with PPSV23 after initial PPSV23 results in lower antibody responses (hyporesponsiveness) for most serotypes compared to the initial dose 2
Clinical Effectiveness Differences
Carriage Reduction
- PCVs reduce nasopharyngeal carriage of pneumococci, creating herd immunity effects beyond direct protection 1
- PPSV23 does not reduce bacterial carriage 1
Age-Specific Efficacy
- PPSV23 is completely ineffective in children under 2 years because they cannot mount adequate immune responses to T-independent polysaccharide antigens 5, 1
- PCVs are effective even in infants due to their T-cell dependent mechanism 1
Functional Antibody Response
- PCV13 demonstrated statistically significantly higher opsonophagocytic activity (OPA) titers than PPSV23 for 8 of 12 shared serotypes in vaccine-naive adults aged 60-64 years 3
- In patients with COPD, PCV7 produced superior functional antibody activity compared to PPSV23 for 6 of 7 serotypes 4
Serotype Coverage
Current Formulations
- PPSV23 covers 23 serotypes (1,2,3,4,5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19A, 19F, 20, 22F, 23F, 33F) 5
- PCV13 covers 13 serotypes 5
- PCV15 covers 15 serotypes (PCV13 serotypes plus 22F and 33F) 6, 7
- PCV20 covers 20 serotypes 5, 6
Coverage vs. Quality Trade-off
- While PPSV23 covers more serotypes numerically, conjugate vaccines provide superior quality protection for the serotypes they do cover 1
Sequential Vaccination Effects
PCV First, Then PPSV23
- Initial vaccination with PCV establishes immune memory that results in robust recall responses when PPSV23 is subsequently administered 2
- Adults initially given PCV13 who later received PPSV23 had significantly higher OPA titers for 10 of 13 serotypes compared to those who received PPSV23 as their first vaccine 2
PPSV23 First, Then PCV
- When PPSV23 is given first, subsequent PPSV23 revaccination yields significantly lower responses for 9 of 13 serotypes compared to initial responses 2
- Current ACIP guidance recommends PCV15 or PCV20 can be given ≥1 year after PPSV23 for adults who previously received only PPSV23 5, 6
Current Recommendations (2023 ACIP)
For Adults ≥65 Years
- Either PCV20 alone OR PCV15 followed by PPSV23 (≥1 year later for most adults, minimum 8 weeks for immunocompromised) 5, 6
For High-Risk Adults 19-64 Years
- Same approach as adults ≥65 years 5
For Children 2-5 Years with Risk Factors
- PCV13 (or PCV15) followed by PPSV23 at least 2 months later 1
Critical Pitfalls to Avoid
- Never use PPSV23 alone in children under 2 years—it provides no protection in this age group 5, 1
- Always administer PCV before PPSV23 when both are indicated to optimize immune response 1, 8
- Do not assume PPSV23's broader serotype coverage makes it superior—the conjugate vaccines' immunologic advantages outweigh the numerical serotype difference 1
- Recognize that prior PPSV23 vaccination and older age reduce responsiveness to subsequent pneumococcal vaccination 2, 4