Paper Title
Monitoring the Immune Landscape against COVID-19 in Japan

Abstract
The COVID-19 immune landscape in Japan was projected, and especially, age-specific fractions immune to SARS-CoV-2 in Japan were examined. Fractions immune to infection substantially varied by age, and vaccination contributed to a substantial decrease in the reproduction number. In addition to the estimation, a waning effect was incorporated using a partial differential equation system. Accounting for the rate at which immunity against symptomatic illness is lost, vaccine-induced and naturally acquired immune fractions were estimated by age group. Future susceptible proportion was shown to be heterogeneous by time and age. Keywords - COVID-19; Vaccination; Epidemiology; Mathematical model; Statistical model