tetano
Editor, Senior Moderator
Clin Microbiol Infect
. 2026 Jul 22:S1198-743X(26)00392-7.
doi: 10.1016/j.cmi.2026.07.025. Online ahead of print.
Assessment of Timing for Influenza Vaccination among Older Adults in Japan: The VENUS Study
Wataru Mimura[SUP] 1 [/SUP], Chieko Ishiguro[SUP] 2 [/SUP], Yosuke Shimizu[SUP] 3 [/SUP], Junko Terada-Hirashima[SUP] 4 [/SUP], Megumi Maeda[SUP] 5 [/SUP], Futoshi Oda[SUP] 5 [/SUP], Haruhisa Fukuda[SUP] 5 [/SUP]
Affiliations
Objectives: In Japan, seasonal influenza vaccination is recommended for older adults between October and mid-December; however, the optimal vaccination timing remains unclear owing to waning immunity and variable epidemic patterns. In this study, we aimed to assess the effectiveness of different vaccination strategies in reducing influenza-related outcomes in older adults.
Methods: Using data from the VENUS Study, we conducted a target trial emulation including adults aged ≥65 years across four influenza seasons (2016/2017, 2017/2018, 2018/2019, and 2019/2020). We applied a cloning, censoring, and weighting approach. Each individual was cloned and assigned to one of seven vaccination strategies at the start of October: no vaccination, vaccination during October, October-November, October-December, November, November-December, or December. Outcomes included influenza, influenza-related hospitalization, and all-cause mortality. Risk ratios (RRs) and risk differences (RDs), relative to no vaccination, were estimated at the end of March for each season based on standardized cumulative incidence.
Results: Annual cohorts included 131,178-138,438 individuals (median age: 76-78 years; male sex: 40.1-41.0%). The influenza incidences and RRs varied by season. Delayed vaccination was associated with the lowest influenza incidence in 2017/2018 and 2018/2019, but not in the other seasons. Influenza-related hospitalizations showed seasonal trends similar to those of influenza. In contrast, early vaccination strategies generally led to reduced all-cause mortality across all seasons. The RRs were 0.80-0.93, 0.80-0.95, 0.82-1.00, and 0.81-0.96 in the 2016/2017, 2017/2018, 2018/2019, and 2019/2020 seasons, respectively. The RDs were larger for mortality than for the influenza-related outcomes.
Conclusions: The effectiveness of each timing strategy varied depending on the outcome and season. Although delayed vaccination was associated with a lower influenza incidence in some seasons, early vaccination generally reduced all-cause mortality.
. 2026 Jul 22:S1198-743X(26)00392-7.
doi: 10.1016/j.cmi.2026.07.025. Online ahead of print.
Assessment of Timing for Influenza Vaccination among Older Adults in Japan: The VENUS Study
Wataru Mimura[SUP] 1 [/SUP], Chieko Ishiguro[SUP] 2 [/SUP], Yosuke Shimizu[SUP] 3 [/SUP], Junko Terada-Hirashima[SUP] 4 [/SUP], Megumi Maeda[SUP] 5 [/SUP], Futoshi Oda[SUP] 5 [/SUP], Haruhisa Fukuda[SUP] 5 [/SUP]
Affiliations
- PMID: 42486303
- DOI: 10.1016/j.cmi.2026.07.025
Objectives: In Japan, seasonal influenza vaccination is recommended for older adults between October and mid-December; however, the optimal vaccination timing remains unclear owing to waning immunity and variable epidemic patterns. In this study, we aimed to assess the effectiveness of different vaccination strategies in reducing influenza-related outcomes in older adults.
Methods: Using data from the VENUS Study, we conducted a target trial emulation including adults aged ≥65 years across four influenza seasons (2016/2017, 2017/2018, 2018/2019, and 2019/2020). We applied a cloning, censoring, and weighting approach. Each individual was cloned and assigned to one of seven vaccination strategies at the start of October: no vaccination, vaccination during October, October-November, October-December, November, November-December, or December. Outcomes included influenza, influenza-related hospitalization, and all-cause mortality. Risk ratios (RRs) and risk differences (RDs), relative to no vaccination, were estimated at the end of March for each season based on standardized cumulative incidence.
Results: Annual cohorts included 131,178-138,438 individuals (median age: 76-78 years; male sex: 40.1-41.0%). The influenza incidences and RRs varied by season. Delayed vaccination was associated with the lowest influenza incidence in 2017/2018 and 2018/2019, but not in the other seasons. Influenza-related hospitalizations showed seasonal trends similar to those of influenza. In contrast, early vaccination strategies generally led to reduced all-cause mortality across all seasons. The RRs were 0.80-0.93, 0.80-0.95, 0.82-1.00, and 0.81-0.96 in the 2016/2017, 2017/2018, 2018/2019, and 2019/2020 seasons, respectively. The RDs were larger for mortality than for the influenza-related outcomes.
Conclusions: The effectiveness of each timing strategy varied depending on the outcome and season. Although delayed vaccination was associated with a lower influenza incidence in some seasons, early vaccination generally reduced all-cause mortality.