Age- and time-dependent waning vaccine effectiveness of PPV23 against community-acquired pneumonia among adults aged 60 and older: A cohort study.

The 23-valent pneumococcal polysaccharide vaccine (PPV23) is recommended for adults to prevent pneumococcal diseases, while its effectiveness over time remains unclear. This study aimed to assess the age- and time-dependent effectiveness of PPV23 in reducing community-acquired pneumonia (CAP) incidence among adults aged 60 and older in China. We conducted a prospective cohort study in Shanghai, China, identifying CAP cases via inpatient and outpatient medical records. Vaccine effectiveness (VE) was estimated using Cox regression models with time-dependent vaccination status, adjusted for demographic characteristics, comorbidities, and seasonal influenza activity. Subgroup analyses stratified by age group, comorbidity status, and observation period were performed. A total of 35,491 participants were included, yielding observation of 158,448 person-years. Overall incidence of CAP was 30.69 (95% confidence interval [CI]: 29.83, 31.57) per 1000 person-years. PPV23 seemed to be ineffective when encompassing all cohort participants in the initial analyses. However, subgroup analyses showed significant adjusted VE for those vaccinated before age 60 (VE = 32.83%, 95% CI: 16.40, 46.03). Significant protection was observed within the first-year post-vaccination (VE = 43.63%, 95% CI: 25.30, 57.47) but declined over time. Furthermore, age-time stratification indicated valid protection for those vaccinated before age 65 within the first year. In addition, VE was higher in those without comorbidities. PPV23 demonstrated modest effectiveness against CAP among those vaccinated before the age of 65 within the first year and decline over time. These findings advocate for prioritizing PPV23 vaccination before age 65 to maximize short-term protection against CAP, underscoring the need for effective booster strategies.