Serotype Shifts Demand Updated Vaccines, Stronger IPD Surveillance

A 12-year surveillance study of invasive pneumococcal disease (IPD) has revealed a shifting serotype landscape that is outpacing current vaccine formulations, according to Human Vaccines & Immunotherapeutics.¹

“Despite remarkable progress in pneumococcal vaccine development, S. pneumoniae remains a significant cause of morbidity and mortality among adults worldwide,” according to authors of a study in Vaccines.² “Advances in conjugate vaccine technology have enabled broader serotype coverage, and recent formulations mark a new era in adult pneumococcal immunization. However, the continuing emergence of nonvaccine serotypes, persistent antimicrobial resistance, and geographic variability in disease burden and vaccination uptake underscore the need for updated, region-specific strategies.”

The current, hospital-based study, tracking 234 cases of IPD over 12 years, highlights the stark clinical manifestations of this persistent pathogen. Researchers found that bacteremia combined with pneumonia was the most frequent presentation, representing 55.6% of cases, and the disease disproportionately affected males and older adults aged 65 years and over.¹

READ MORE: Serotype 4 IPD Threat for Young Adults, Unvaccinated Men

The Clinical Reality of Shifting Serotypes

Among the identified vital strains, serotypes 3 and 8 emerged as the most prevalent culprits overall. This matches broader international data, but the local dynamics offer a warning about serotype replacement, the process by which vaccines successfully suppress target strains only for non-vaccine strains to fill the ecological void.

Although pediatric vaccination campaigns successfully reduced traditional vaccine-preventable cases, vaccinated adults in the Italian study were increasingly infected by serotypes 15A and 15C, which are not covered by the standard 13-valent pneumococcal conjugate vaccine (PCV13).¹

Similarly, a comprehensive narrative review of IPD in North Africa and the Middle East documented that despite PCV13 serotypes declining after vaccine introduction, infections caused by non-vaccine serotypes rose or remained high.³

Rising Resistance and the Antimicrobial Stewardship

Beyond the shifting distribution of serotypes, clinicians and pharmacists face a growing threat from antimicrobial resistance.¹

The surveillance study detected macrolide resistance in 26.9% of all isolated pneumococcal strains, while beta-lactam resistance was found in 14.9%. Just under 40% of the highly prevalent serotype 3 strains exhibited macrolide resistance, while serotype 19F demonstrated dual resistance to both penicillin and macrolides in 66.7% of evaluated cases.

These findings underscore why WHO has designated penicillin-nonsusceptible S. pneumoniae as a priority pathogen and why pneumococcal vaccination is increasingly viewed as a core component of antimicrobial stewardship. As selective pressure from antibiotics and older vaccines drives capsular switching and the proliferation of resistant lineages, next-generation vaccines with expanded valencies are becoming critical.²

Conjugate formulations targeting emerging resistant serotypes, such as PCV15, PCV20, and the recently approved PCV21, offer a crucial tool to prevent infections before they require antibiotic treatment, thereby mitigating the spread of resistant strains.^2,4

Pharmacists at the Frontline of Prevention

For community pharmacists, these microbiological shifts translate directly to patient care decisions.⁵

A qualitative study exploring pneumococcal vaccination in rural pharmacies highlighted that although pharmacists are uniquely positioned to increase vaccine uptake, they are heavily burdened by the complexity of frequently changing guidelines and the sheer variety of vaccine products. Staffing constraints, incomplete state immunization registries, and high stocking costs for vaccines sold only in bulk further complicate proactive immunizations in the pharmacy workflow.

Yet, the benefits of pharmacist-led intervention are profound, both clinically and economically. The Italian hospital data demonstrated that vaccinated patients with IPD had a median hospital stay of just 8 days compared with 16 days for unvaccinated patients, translating to significantly lower median health care costs.^1,5

Policy updates in countries like Australia, which transitioned childhood schedules to PCV20 and adult schedules to PCV21 while phasing out the older 23-valent polysaccharide vaccine, show a global trend toward simplifying immunization schedules.^4,5

By staying informed of these guideline evolutions and actively counseling patients, pharmacists can shut down regional reservoirs of nonvaccine serotypes and play a decisive role in curbing the IPD burden.^2,3

“IPD surveillance is critical to inform prevention strategies,” concluded the authors.¹ “Our findings quantify how much vaccination reduces disease severity and health care costs but highlight gaps in vaccine coverage against emerging serotypes due to replacement mechanisms.”

READ MORE: Pneumococcal Resource Center

REFERENCES

1. Vecchio R, Iskandar E, Gentile L, et al. Invasive pneumococcal disease burden, clinical characteristics, serotypes' distribution, immunization status and antimicrobial resistance: evidence from 12-year hospital-based surveillance and cost analysis. Hum Vaccin Immunother. 2026 Dec;22(1):2670827. doi: 10.1080/21645515.2026.2670827

2. Ozisik L. The new era of pneumococcal vaccination in adults: What is next? Vaccines (Basel). 2025 May 7;13(5):498. doi: 10.3390/vaccines13050498

3. Haridy H, Dbaibo G, Jeena P, et al. A narrative review of pneumococcal serotypes causing invasive disease in North Africa and the Middle East. Vaccine X. 2025;25:100688. doi:10.1016/j.jvacx.2025.100688

4. Pneumococcal vaccines – frequently asked questions (FAQs). National Centre for Immunisation Research and Surveillance. July 1, 2026. Accessed August 26, 2026. https://ncirs.org.au/ncirs-fact-sheets-faqs-and-other-resources/pneumococcal-vaccines-frequently-asked-questions-faqs

5. Vieira LEB, Marley GT, Hastings TJ, et al. Barriers and facilitators to pneumococcal vaccination in rural community pharmacy: a qualitative study. Vaccine X. 2026;29:100786. doi:10.1016/j.jvacx.2026.100786