Incidence of medically attended influenza and influenza virus infections confirmed by serology in Ningbo City from 2017-2018 to 2019-2020.

We identified substantial outpatient influenza burden in all ages in Ningbo. Our cohort study limited in elderly people found that this age group had a high risk of seasonal influenza infections. Our study informs the importance of increasing influenza vaccine coverage in high-risk population including elderly people.