The incidence of invasive pneumococcal disease (IPD) in adults has decreased considerably over the past few decades. According to the US Centers for Disease Control and Prevention (CDC), the number of IPD cases in adults between the ages of 19 and 64 went from 16 per 100,000 people in 1998 to just 7 per 100,000 people in 2015.¹ How has this happened?

One reason is the availability of the 13-valent pneumococcal conjugate vaccine (PCV13) and the 23-valent pneumococcal polysaccharide vaccine (PPSV23). PCV13 has been used as a vaccine for children in Japan since 2013, replacing the 7-valent pneumococcal conjugate vaccine, and the indirect impact of these vaccines may have been a decrease in adult IPD. What about PPSV23?

Vaccines like PPSV23 target specific serotypes of Streptococcus pneumoniae, so its effectiveness may depend on which serotype the patient has. Recently, Emerging Infectious Diseases published a study in which data from thousands of Japanese adults with IPD were assessed to gauge the effectiveness of PPSV23.² Since 2013, physicians in Japan have had to report the information of all patients with IPD to the nearest public health center. Using data from 1121 eligible patients with IPD from April 2013 to December 2017, the researchers used an indirect cohort method to calculate the effectiveness of PPSV23. Patients were divided into 2 groups: those who had IPD caused by a serotype that PPSV23 targets (66.5%; serotypes 1, 2, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19A, 19F, 20, 22F, 23F, 33F) and those with IPD from non-PPSV23 serotypes (33.5%; control).

Median age was 70. Although 27% of the PPSV23 group had no previous underlying conditions, 64% of them had clinical manifestations of pneumonia. Two-thirds of the PPSV23 group had IPD in autumn or winter, which are seasons with a generally higher incidence of IPD. In both the PPSV23 group and the control group, there was a separate fatal outcome in 18% of patients.

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Overall effectiveness of PPSV23 was 42.2% after adjusting and controlling for confounders; the effectiveness of PPSV23 against serotypes 19A, 12F, and 10A was more than 70%, but the vaccine was found to be 22.7% effective against serotype 22F and 22.4% effective against serotype 7F.

The researchers also divided the cohort into those treated from 2013 to 2015 and those treated from 2016 to 2017. The effectiveness of PPSV23 in the first group was 47.1%, while the effectiveness of the vaccine in the second group was 39.3%. The effectiveness of PPSV23 in patients aged 65 and older was less but more consistent (39.9% from 2013 to 2015, 39.4% from 2016 to 2017). Although the vaccine was found to be less effective in these older patients, the outcome may be attributed to decreased immunity to pneumococcal polysaccharides with advanced age.

The researchers concluded that the effectiveness of PPSV23 is moderate, but not significant enough to be attributed to the overall decrease in IPD of late.


  1. Pneumococcal Disease: Surveillance reporting and trends. Centers for Disease and Control website. Reviewed September 6, 2017. Accessed November 18, 2020.
  2. Shimbashi R, Suzuki M, Chang B, et al; for the Adult IPD Study Group. Effectiveness of 23-valent pneumococcal polysaccharide vaccine against invasive pneumococcal disease in adults, Japan, 2013–2017. Emerg Infect Dis. 2020;26(10):2378-2386. doi:10.3201/eid2610.191531