Abstract Background Gastric cancer has historically been driven by long‑standing Helicobacter pylori infection. The nationwide expansion of H. pylori eradication therapy beginning in 2013 created a unique opportunity to evaluate its population‑level impact on gastric cancer mortality. However, short‑term mortality trends following eradication are difficult to interpret because they reflect overlapping influences of ageing, cohort replacement, and cumulative infection history. This study aimed to provide a model‑based, population‑level assessment of the early impact of eradication during the first decade of nationwide implementation. Methods We applied a two‑layer analytic framework consisting of a counterfactual analysis comparing observed mortality during 2013–2021 with expected mortality had eradication uptake remained at pre‑2013 levels, combined with a structured state‑transition (Markov) model with time‑dependent parameters. To estimate annual gastric cancer deaths prevented and the proportion of mortality reduction attributable to eradication, the model integrated age‑specific biological hazard, cumulative infection history, cohort‑specific H. pylori prevalence, and annual changes in eradication uptake. Results Observed gastric cancer deaths declined from 48,632 in 2013 to 41,624 in 2021, whereas counterfactual gastric cancer deaths declined more modestly, from 49,779 to 49,453. The divergence between observed and counterfactual deaths steadily widened from 1,147 in 2013 to 7,829 in 2021. Model‑based estimates indicated that eradication prevented 6,461 gastric cancer deaths during 2013–2021, with annual deaths prevented increasing from 165 in 2015 to 1,604 in 2021, particularly among adults aged 60–79, who showed the most pronounced early benefit reflecting cumulative infection history and real-world uptake patterns. Conclusions The early population‑level impact of H. pylori eradication is consistent with a 16% reduction in gastric cancer deaths by 2021. These findings provide real‑world insight into how primary prevention can shape short‑term national cancer trends. This approach offers a quantitative framework to inform future prevention strategies in high‑prevalence settings seeking to evaluate early implementation effects.
Akiko Kowada (Mon,) studied this question.