key: cord-0937433-motzhbew
authors: Xia, Zhi; Yang, Lin; Li, Na; Nie, Bo; Wang, Hong; Xu, Hui; He, Daihai
title: Seasonal influenza activity in young children before the COVID‐19 outbreak in Wuhan, China
date: 2020-09-01
journal: Transbound Emerg Dis
DOI: 10.1111/tbed.13799
sha: e3c52fb57d8bb2ff68d0df62d77880531d1c9380
doc_id: 937433
cord_uid: motzhbew

The activity of influenza A at the end of 2019 was higher than previous two years in children younger than 6 years old in Wuhan, China. The 2019–2020 winter peak of seasonal influenza preceded the COVID‐19 outbreak, with a higher and earlier peak than those of the 2017–2018 and 2018–2019 seasons. We speculate this could be due to the earlier CNY holiday season in 2019–2020 than in previous two years. We compared these results with those of two previous studies to further discuss the possible interference between influenza and COVID‐19 in young children.

During the first wave of COVID-19 in China, the attack rate of coronavirus disease 2019 in children was much lower than in adults, and most child cases had mild symptoms (Dong et al., 2020) . However, the secondary attack rate of COVID-19 among close contacts was later found similar between children and other age groups (Bi et al., 2020) . In Wuhan, Hubei province, China, there was only one paediatric case of COVID-19 officially reported before 22 January 2020. The reasons why children were exempted from COVID-19 infection in the early stage remain unclear. One hypothesis is the potential interference of seasonal influenza peaks with the newly-emerging COVID-19 outbreak among young children. Liu et al reported that 11% and 1.6% of 366 hospitalized children (≤16 years of age) were infected by influenza and SARS-CoV-2, respectively, in early January 2020 in Wuhan, China. Kong et al found that the incidence rate of influenza-illness-like (ILI) was substantially higher in the 2019-2020 season than in the previous two years based on the surveillance data in two hospitals in Wuhan, China. The retrospective laboratory tests in the specimens from these ILI patients to January 2020 showed that an outbreak of seasonal influenza attacked the ≤30 age group in October-November 2019, followed by the COVID-19 cases in the >30-years of age group that first emerged in December 2019 to January 2020. Surprisingly, no COVID-19 case was found in the ≤30 age group in their 120 samples (Table 1) .

Kong et al and Liu et al, as one would expect some COVID-19 cases among the young age group of ILI patients by the mid-January in Wuhan, China.

We obtained the test results of 194,672 specimens from the Maternal and Child Health Hospital of Hubei Province in Wuhan.

These specimens were collected from 1 January 2017 to 20 May 2020, for immunofluorescence tests of influenza type A and B.

Around 75% of the specimens were taken from the outpatients and inpatients aged ≤6 years old. In consistent with the findings by Kong et al, we also found a peak of influenza A in early January, coinciding with the start of the COVID-19 outbreak. It is interesting to note that the winter peak of seasonal influenza in Wuhan appeared in We observe a sudden drop of influenza A cases in early January 2020, presumably due to social distancing and avoidance of hospital visits immediately after the official report of pneumonia clusters of COVID-19 and closure of the Huanan Seafood market on 31

December 2019 (Figure 1 ).

Infection risk of COVID-19 was known to increase with age (Sun, Chen, & Viboud, 2020) . If we assume that the ratio of COVID-19 to influenza cases in the <30 age group was not less than that in the <16 age group and similar across different hospitals, we could derive a ratio of 0.136 (1.6%/ 11.80%) based on reference . Given the influenza positive rate of 60% from reference (Kong et al., 2020) , we would expect that around 8% of COVID-19 would have occurred in ILI patients under 30 years old. Hence, the chance of having zero COVID-19 case in the <30 age group of ILI cases, as reported in reference (Kong et al., 2020) , was estimated to be very low ( CoV-2, particularly in children.

Research project. Other authors declare no conflict of interest.

All authors conceived and conducted the research and wrote the draft. All authors critically revised the manuscript, and all authors approved the submission.

The ethical approval has been obtained from the Maternal and Child

Health Hospital of Hubei Province. Individual consents were exempted as the aggregated data were used in this study.

All data used are from public domain.

Lin Yang https://orcid.org/0000-0002-5964-3233

Daihai He https://orcid.org/0000-0003-3253-654X

Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: A retrospective cohort study. The Lancet Infectious Diseases

Epidemiological characteristics of 2143 pediatric patients with 2019 coronavirus disease in China

SARS-CoV-2 detection in patients with influenza-like illness

Detection of Covid-19 in children in early

Early epidemiological analysis of the coronavirus disease 2019 outbreak based on crowdsourced data: A population-level observational study. The Lancet Digital Health