Estimated incidence of influenza in Guangzhou, China, 2019-2022

Influenza is a significant public health issue, particularly for vulnerable groups like children and the elderly. Despite widespread vaccination and public health measures, age-specific incidence data-crucial for targeted interventions-are limited in many areas, including Guangzhou. The epidemiological patterns of influenza have also been affected by non-pharmaceutical interventions during the COVID-19 pandemic, underscoring the need for updated local estimates. This study aimed to estimate the age-specific incidence of influenza infection in Guangzhou from 2019 to 2022-a period covering both pre-pandemic and pandemic phases-to inform regionally tailored prevention and control strategies.

This study analyzed surveillance data on influenza-like illness (ILI) and virological test results from sentinel hospitals in Guangzhou covering the period from 2019 to 2022. A previously established multiplier model was employed, which integrated age-specific consultation rates, influenza positivity rates, as well as parameters related to symptom presentation and detection sensitivity. Monte Carlo simulations were utilized to estimate annual age-stratified influenza infection and incidence rates, accompanied by 95% confidence intervals. The population denominators were derived from the national census conducted in 2020.

7.78% of the total population in Guangzhou were infected by influenza in 2019, 1.40% in 2020, 1.85% in 2021 and 12.13% in 2022 and incidence rates were 5.15% in 2019, 0.93% in 2020, 1.23% in 2021 and 8.04% in 2022. The highest influenza infection and incidence rates were observed in 2022 and the lowest in 2020. Infections in the 0-14 age group were 27.19%, 3.57%, 11.16% and 66.15% during 2019-2022 and respective incidence rates were 18.00%, 2.37%, 7.41% and 43.84%.

0-14-year-old infants and children were the main victims of influenza. Targeted strategies should be developed to prevent the spread in this age group.