Impact of a 21-valent pneumococcal conjugate vaccine on pneumococcal disease incidence among adults 65–84 years of age in Belgium: An epidemiological modeling study

Pneumococcal disease (PD) imposes a high clinical and economic burden in Belgium. Effective multivalent vaccines are available and recommended for adults at elevated risk of PD, but do not protect against certain clinically important bacterial serotypes. In response, a new 21-valent pneumococcal conjugate vaccine, PCV21, was designed to protect adults against a greater proportion of pneumococcal disease. This study estimated the impact of implementing PCV21 versus the currently recommended vaccine (PCV20) in Belgium on the incidence of invasive PD (IPD) and non-bacteremic pneumococcal pneumonia (NBPP) among adults aged 65-84 y. We updated a published dynamic transmission model using Belgian data. Model outputs included the annual incidence and cumulative number of cases of IPD, inpatient NBPP, and outpatient NBPP among adults 65-80 and 81-84 over a 15-y time horizon. Adult vaccination using PCV21 was predicted to reduce the incidence and number of PD cases among adults aged 65-84, compared to vaccination using PCV20. Among adults aged 65-80, replacing PCV20 with PCV21 was estimated to reduce the incidence of IPD by 3.68%, inpatient NBPP by 3.08%, and outpatient NBPP by 3.34% by 2036, equating to 134 fewer IPD cases and 1,195 fewer NBPP (inpatient and outpatient) cases over 15 y. Slightly smaller relative differences in disease incidence between vaccination strategies were observed for adults aged 81-84, although PCV21 still prevented substantial additional cases compared to PCV20. Overall, replacing PCV20 with PCV21 in the Belgian adult pneumococcal vaccination program was predicted to avert additional cases of PD among adults 65-84 y.