Less Common Pneumococcal Serotypes Cause More Severe Community-Acquired Pneumonia

Certain serotypes included in the pneumococcal 20-valent conjugate vaccine (PCV20) can cause more severe community-acquired pneumonia (CAP) while being of relatively lower prevalence among the population, according to research presented by investigators at IDWeek. The meeting took place from Oct. 19 to Oct. 22, 2025, in Atlanta, GA.¹

Determining Serotypes Causing CAP is Critical for Public Health

The presentation of CAP can differ based on the serotype causing infection. Different serotypes have been associated with varying levels of virulence and invasiveness. Numerous vaccine options, including PCV20, are available to protect against serotypes that can cause CAP. Since the proliferation of these vaccines, the serotype distribution of CAP has fluctuated, necessitating reviews of CAP serotype characteristics and prevalence.¹

In the current trial, authors described clinical and demographic aspects of CAP cases by serotype for those included in PCV20. Previously collected data from adults aged 18 and older hospitalized with CAP from a series of US-based sites between 2014 and 2016 and 2019 and 2020 were collected. Serotyping was performed using blood cultures and respiratory specimens, and serotype-specific urinary antigen detection assays were used to detect serotypes.¹

Common PCV20 serotypes observed by the investigators were 19A, 3, 22F, 11A, and 5. The highest proportion of severe outcomes in patients were due to serotypes 1, 3, 6A/6C, and 23F—described as exhibiting a pneumonia severity index score of 4 or 5—and 9V, 12F, and 23F—characterized by intensive care unit admission. Notably, all serotypes but 6B, 8, and 19F were associated with mortality.¹

CAP cases due to serotypes 6A/C, 12F, and especially 15B/C had higher proportions of bacteremia, while those infected with serotypes 1, 10A, and 23F had the longest hospital stay. Compared with the other serotypes, cases of 19F and 1 were enriched for patients aged 18 through 49 years, and 4 and 6A/6C for patients aged 65 and older. Cases caused by serotype 15B/C occurred proportionally more among Black patients, according to the investigators.¹

What Should Health Care Professionals Know?

These insights demonstrate how certain serotypes of Streptococcus pneumoniae can induce more severe CAP, despite being of lower prevalence. Although the pathogen responsible for disease can be determined in some patients, for most of them, the cause of their CAP can remain unknown. Given these complexities in establishing the individual cause of many CAP cases, encouraging vaccination to prevent serious disease is crucial, especially with pneumococcal conjugate vaccines.²

The use of serotype-specific urinary antigen detection (SSUAD) assays can revolutionize the detection capabilities of public health officials. Research has shown that SSUAD testing can significantly increase the detection of pneumococcal pneumonia among individuals hospitalized with CAP. This research centered around the detection of serotypes in the pneumococcal 13-valent conjugate vaccine but could be applied to other vaccine serotypes, including PCV20 and the pneumococcal 21-valent conjugate vaccine.³

As newer pneumococcal vaccines are developed, continued surveillance and monitoring of serotypes primarily causing CAP in the adult population is critical. It is also important for health professionals to recognize that Streptococcus pneumoniae is not the only known cause of CAP. In fact, since the widespread use of antibiotic and the introduction of pneumococcal vaccines, the estimated proportion of pneumococcal-caused CAP has declined.³

Pharmacists are in a critical position to counsel and advocate for patients on the benefits of pneumococcal vaccination. Older adults and those with underlying medical conditions are at heightened risk of serious outcomes if infected, including the development of CAP, so immunization advocacy should be centered around those populations.

REFERENCES

1. Grant L, Vojicic J, Ali M, et al. (P-654) Demographic and clinical characteristics, by pneumococcal serotype, of adults hospitalized with community-acquired pneumonia in the United States. Presented: IDWeek; October 20, 2025; Atlanta, Georgia. Accessed Online via IDWeek Virtual Platform on November 5, 2025.

2. Wunderink RG, Self WH, Anderson EJ, et al. Pneumococcal community-acquired pneumonia detected by serotype-specific urinary antigen detection assays. Clin Infect Dis. 2018;66(10):1504-1510. doi:10.1093/cid/cix1066

3. Grijalva CG. What fraction of adult community-acquired pneumonia is caused by the pneumococcus? New insights from Spain. Clin Infect Dis. 2021;73(6):1086-1088. doi:10.1093/cid/ciab314