Characteristics of Seasonal Influenza Virus Activity in a Subtropical City in China, 2013–2019

Abstract

Background: To optimize seasonal influenza vaccination programs in regions with potentially complicated seasonal patterns, the epidemiological characteristics of seasonal influenza activity in a subtropical city of China were explored. Materials and Methods: Influenza virus data of patients with influenza-like illness (ILI) during 2013-2019 were collected from two sentinel hospitals in a subtropical region of China, Yichang city. The influenza virus positive rate among sampled ILI cases served as a proxy to estimate influenza seasonal characteristics, including periodicity, duration, peaks, and predominant subtypes/lineages. Epidemiological features of different years, seasons and age groups were analyzed, and vaccine mismatches were identified. Results: In total, 8693 ILI cases were included; 1439 (16.6%) were laboratory-confirmed influenza cases. The influenza A positive rate (10.6%) was higher than the influenza B positive rate (5.9%). There were three influenza were both mismatched with the influenza B component of the trivalent vaccine. Children 5-14 years old (26.4%) and individuals over 60 years old (16.9%) had the highest influenza positive rates. Conclusions: The seasonal epidemic period and the predominant subtype/lineage of influenza viruses in Yichang city are complex. Influenza vaccination timing and strategies need to be optimized according to the local features of influenza virus activity.

Spatial timing of circulating seasonal influenza A and B viruses in China from 2014 to 2018

“…The start of an influenza epidemic period was defined as the first week during which the positive rate of influenza virus testing was higher than 10% and stayed above that level for at least four consecutive weeks. The end of an influenza epidemic period was defined as the first week during which the positive rate was lower than 10% and stayed at that level for at least four consecutive weeks 19 . Based on influenza activity, climate, and geography, we divided China into two distinct regions, north and south, for the analysis and interpretation of influenza surveillance data.…”

Epidemic patterns of the different influenza virus types and subtypes/lineages for 10 years in Chongqing, China, 2010–2019

“…During the study period, children aged 5–14 years had the highest proportion of positive influenza specimens (36.33%) among all age groups, which was consistent with previous studies. 12–15 This phenomenon may stem from the majority of children aged 5–14 years being students who attend school in densely populated classrooms with limited ventilation, have poor hygiene and disease prevention awareness, and are more susceptible to influenza transmission due to their young age and weak immunity, leading to a high incidence of influenza. Therefore, influenza prevention and control measures should be prioritized at the levels of schools and childcare institutions, with a focus on strengthening health education and implementing effective protective measures including targeted influenza vaccination campaigns.…”

“… 26–29 Our results showed that influenza epidemics in Chongqing tend to occur in spring and winter but influenza B viruses were primarily dominant in the spring season. 10 , 12 During this period, the public should pay attention to non-pharmaceutical prevention measures, such as washing hands, wearing masks, opening windows for ventilation frequently.…”

The 2 nd China Vaccinology Integrated Innovation & Teaching Development Conference: Promoting the construction of vaccinology discipline system

“…The mechanism will provide innovative models and standards for other regions to conduct disease surveillance and issue early warnings. 24 , 25 …”