Pneumococcal vaccination, but not influenza vaccination, is negatively associated with incident dementia among Japanese older adults: The JAGES 2013–2022 prospective cohort study

•The uptake of PPSV23 in older adults was negatively associated with incident dementia who required daily living care.•Such associations were observed regardless of the follow-up period or influenza vaccination.•The uptake of IIV was not associated with incident dementia, regardless of the follow-up period or PPSV23.•PPSV23 was independently associated with incident dementia, whereas the IIV was not. It is unclear whether inactivated influenza vaccination (IIV) or pneumococcal vaccination are associated with the risk of dementia; however, both types of vaccination are recommended for older adults. Studies have shown that the IIV is negatively associated with incident dementia; however, the uptake of pneumococcal vaccinations has not been considered. We investigated the independent associations of IIV and 23-valent pneumococcal polysaccharide vaccine (PPSV23) with incident dementia in older adults. Health-related information on older Japanese adults was obtained through a baseline survey conducted in 2013 (baseline survey). The uptake of IIV and PPSV23 was determined in a second survey conducted in 2016 (second wave). Both surveys were conducted among independent Japanese older adults aged ≥ 65 years at the two surveys and who had not been certified as needing long-term care (LTC). In the second wave, 9,865 participants were followed up for 3.5 years (short-term follow-up), and 6,995 participants were followed up for six years and five months (long-term follow-up) until they required LTC due to dementia onset (incident dementia). A competing risk model with stabilized inverse probability weighting (SIPW) was constructed to calculate the hazard ratios (HRs) and 95 % confidence intervals (CIs) of incident dementia. PPSV23 uptake was negatively associated with incident dementia among participants in both the short- and long-term follow-up periods after SIPW (short-term follow-up: HR: 0.77, 95 % CI: 0.63 – 0.95; long-term follow-up: HR: 0.83, 95 % CI: 0.70 – 0.97). Conversely, IIV uptake was not associated with incident dementia among participants in either follow-up group (short-term follow-up: HR: 0.86, 95 % CI: 0.63–1.16; long-term follow-up: HR: 0.99, 95 % CI: 0.76–1.29). The PPSV23 uptake was negatively associated with incident dementia in participants without the IIV uptake (short-term follow-up: HR: 0.44, 95 % CI: 0.24 – 0.81; long-term follow-up: HR: 0.47, 95 % CI: 0.29 – 0.76). Conversely, the IIV uptake was not associated with incident dementia regard