Epidemiological analysis of influenza during COVID-19 epidemic in Jiangsu Province from 2020 to 2022

Abstract

By analyzing the epidemic characteristics of influenza during the COVID-19 epidemic in Jiangsu Province from 2020 to 2022, it found that 90 721 influenza-like case samples were collected in Jiangsu Province from 2020 to 2022, of which 6 732 were nucleic acid-positive samples, with an average positive detection rate of 7.4% in three years. The annual positive detection rate presented a U-shaped distribution, with positive detection rates of 4.4%, 3.2% and 14.7%, respectively, with statistically significant differences (χ2=12 126.00, P<0.001). During the seasonal peak period of influenza from 2020 to 2022, there was a significant decrease in the intensity of the two influenza activity peaks that occurred before the virus became fully prevalent in the population. The first peak occurred from January to February 2020, and the positive detection rate of influenza nucleic acid decreased from 54.4% (317/583) in the third week to 2.1% (12/584) in the eighth week, with a statistically significant difference (χ2=394.49, P<0.001). The second occurred in December 2022, and the positive detection rate of influenza nucleic acid decreased from 14.9% (90/605) at the 49th week to 1.9% (11/572) at the 52nd week, with a statistically significant difference (χ2=62.88, P<0.001). The influenza epidemic in Jiangsu Province from 2020 to 2022 had obvious seasonal characteristics, and the distribution differences of influenza virus-positive cases in each month were statistically significant (χ2=858.00, P<0.001), with two epidemic peaks each year: winter, spring (December to March of the following year), and summer, and autumn (July to November). The epidemic strains were the B-V strain and seasonal H3 strain, respectively. There was a statistically significant difference in the positive detection rate of influenza cases detected in different age groups (χ2=60.00, P<0.001). The age group between 5 and 14 years old had the highest influenza-positive detection rate (10.4%), while the age group≥60 years old had a relatively low influenza-positive detection rate (5.1%). The positive detection rate decreased with the increase in the age group (Ztrend=12.82, P<0.001).