Differences on Pyrexia Related Immune Responses Between COVID-19 and Inuenza A Children

Background: Coronavirus disease-2019 has brought rapid challenge to the current health care system raising millions of infected patients globally. The clinical manifestations of asymptomatic patients especially children and young people will contribute to the management of current pandemic. Methods: To provide precise and comprehensive information on the less symptomatic COVID-19 children, total 62 hospitalized children aged 1-14 years with conrmation infection of either SARS-CoV-2 or inuenza A were enrolled for past half of year from September 2019 to February 2020. The epidemiological, demographic, clinical, radiologic and laboratory ndings were extracted from the electronic medical records of the patients. Results: We reported less fever (43.33% vs 100%, p<0.001) with lower body temperature (p<0.001) and hypoinammatory responses occurred in COVID-19 children in comparison with inuenza infection. We further showed the signicant correlations between initial body temperature and multiple immune parameters to imply the role of thermoregulation on asymptomatic COVID-19 children. Conclusions: COVID-19 children were more likely to have mild symptoms and relatively slow progression. Furthermore, correlations between initial body temperature and immunological functional parameters suggested that non-susceptibility of children to SARS-CoV-2 virus may lie in the low sensitivity on thermal regulation of immune activation. 95% CI. While for data not normally distributed, median with interquartile range (IQR) is used. Categorical variables are given as counts and percentages.


Introduction
The escalating epidemic of Coronavirus Disease 2019 (COVID-19) has spanned over the world resulting in millions of con rmed cases and hundreds of thousands of death globally. According to the published data, predominance of child and younger teen COVID-19 patients represented mild symptom 1 with less than 1% of con rmed cases 2 . Several studies had given the glance at the epidemiological characteristics of COVID-19 con rmed children 3 . Here we provide precise and comprehensive comparisons on SARS-CoV-2 infected children and in uenza A virus patients to elucidate the relationship between thermal activation and immune responses in the asymptomatic COVID-19 infection.

Methods
In this retrospective cohort study, medical records of admitted children aged from 1 to14 years with laboratory con rmation of either SARS-CoV-2 or in uenza A infection were collected from September 2019 to February 2020. Total 30 SARS-CoV-2 and 32 in uenza A con rmed cases were enrolled in this past half of year. Con rmed SARS-CoV-2 or in uenza A infection was de ned as detection of virus RNA by the real-time uorescent polymerase chain reaction (PCR) in pharyngeal swabs. Fever was de ned as an axillary temperature of 37.5°C or higher. Comparisons were conducted by using the Mann-Whitney non-parametric test. Mean ±standard deviation (SD) and 95% con dence interval were reported for normally distributed, continuous variables. Categorical variables were reported as counts and percentages. While for data not normally distributed, median with interquartile range (IQR) was used.
Pearson correlation coe cients were used to assess the relation of in ammatory parameters and body temperatures. All statistical analysis was done on SPSS version 25.

Results
The median age of 30 COVID-19 con rmed children was 5.29 years (IQR: 3.04-7.61), while that of 32 in uenza A infected children was 7.09 years (4.08-11.05) (shown in Table 1). Overall, 63.33% of COVID-19 children were girls and the in uenza A group showed the opposite portion with 59.38% of boys. Comparison on onset symptoms showed that instead of 100% exhibition of both fever and cough in in uenza A infected children, only 43.33% (p<0.001) and 26.67% (p<0.001) patients represented fever and cough respectively in COVID-19 infected cases.
On admission day, lymphocyte count and serum lactate dehydrogenase (LDH) were elevated dramatically beyond the normal ranges in both two groups. One the other hand, compared with extremely higher levels of serum C-reactive protein (CRP), procalcitonin (PCT) as well as erythrocyte sedimentation rate (ESR) in in uenza A infected children, those of COVID-19 patients were considered within the normal ranges.
Once they were admitted to hospital, total (100%) in uenza A patients represented fever with the average body temperature of 39.5℃ (39.3-39.7℃). While only 13 (43.3%) COVID-19 children exhibited with fever on the signi cantly lower (p<0.001) average body temperature of 38.3℃ (37.8-38.8℃). After 3 days of hospital stay, there remained 23 in uenza A patients with continuous fever on average of 38.8℃ (38.5-39.1℃). In contrast, only 5 COVID-19 children's body temperature were hotter than 37.5℃ (shown as Figure 1A & B). Simultaneously, with 3 days of hospital care, the in uenza A infected children represented with signi cantly decreased WBC, neutrophil and lymphocyte counts (shown as Figure 1C-E). On the contrary, there is nearly no change on those of COVID-19 patients. Remarkably, both patients showed obviously elevated platelet levels (shown as Figure 1F). Besides, radiographical imaging indicated that typical pneumonia patterns of initial 23 (71.88%) in uenza A patients predominately had obvious improvements in 3-5 days. In contrast, 9 (30%) OCIVD-19 children showed few changes in extent of the ground-glass opacities and another 2 children represented increased parenchymal density. Subsequently, all in uenza A patients recovered after an average of 5.31 days (4.58-6.04) of hospitalization. 7 COVID-19 children were still in hospital with 15 to 21 days of current stays and the average length of hospital stay was 15.53 days (13.91-17.16).
Further pearson correlation analysis indicated that there were substantially signi cant positive correlations between the degree of body temperature and these immunological parameters on admission day for COVID-19 patients (shown in Table 2, WBC: r=0.414, p=0.028; HB: r=-0.387, p=0.042; CRP: r=0.509, p=0.011; PCT: r=0.51, p=0.013). Dissimilarly, only admission PCT level was signi cantly correlated with the body temperature of in uenza A children.

Discussion
COVID-19 disease in adults was typically identi ed with severe interstitial pneumonia and subsequent acute respiratory distress syndrome by hyperactivation of the in ammatory cascade 1,4 . As for COVID-19 children patients, most of them were more likely to have mild symptoms 5 with different epidemiological characteristics 6 , clinical manifestations 7 , as well as transmission patterns 8 from adult patients, probably due to the weaker immune response 9 . We described the COVID-19 children with lower body temperature and signi cantly lower neutrophil count, as well as attenuated CRP and PCT levels in comparison with in uenza A children. We further elucidated the signi cant correlations between initial body temperature and multiple immune functional parameters in COVID-19 children instead of in uenza kids. These ndings offer some clue to differing pathogenesis of COVID-19 for further study. In addition, corresponded with recent COVID-19 children cases of the development of high fever and cytokine storm in Kawasaki disease 10 , our results clarify the less activated immune status in asymptomatic COVID-19 children and suggested that non-susceptibility of children to SARS-CoV-2 virus may lie in the low activity of immune response. Further explorations will contribute to the management and development of therapeutics for COVID-19 patients.
Some limitations should be considered. First, in uenza A data was collected from almost 5-month span, while that of COVID-19 cases were derived from recent two months affected by the outbreak of COVID-19 pandemic, which probably resulted in unavoidable bias. Second, in this retrospective study, COVID-19 con rmed cases were originated from several hospitals in Shenzhen, China, subsequently transferred to Shenzhen Third People's Hospital for quarantine and medical treatment. Whereas in uenza A data came from an independent single center. Data collection of the similar cohort would be better to avoid statistical disequilibrium.

Conclusion
By comprehensive comparison on clinical characteristics of COVID-19 children and in uenza A infected children, our study revealed that COVID-19 children were more likely represented as asymptomatic and mild cases with subclinical manifestations and relatively slow progression. Furthermore, correlations between initial body temperature and immunological functional parameters suggested that nonsusceptibility of children to SARS-CoV-2 virus may lie in the low sensitivity on immune activation. This study was approved by Shenzhen Third People's Hospital Ethics Committee and informed consent in in uenza cohort was obtained from parents or guardians. For COVID-19 patients, written informed consent was waived by the Ethics Commission. Any data we collected and analyzed was derived from clinical raw record without any intervention and in uence on clinical treatment. And no additional collection of human sample or genetic resource materials was performed in our study.

Consent for publication: Not applicable
Availability of data and materials: The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Con ict of interest:
No nancial or non nancial bene ts have been received or will be received from any party related directly or indirectly to the subject of this article.

Funding source:
This work was supported by Sanming Project of Medicine in Shenzhen (SZSM201512005).

Authors' contributions:
Shanglong Kou and Senlin Zhan contribute equally to this work. Jing Yuan and Yanchao Pan are cocorresponding authors. Shanglong Kou, Yanchao Pan conceptualized and designed the study, carried out the initial analyses, and drafted the initial manuscript. Senlin Zhan and Guofang Deng designed the data collection instruments, collected data and revised the manuscript. Xiaohe Li, Mingxia Zhang and Jing Yuan supervised data collection, and critically reviewed the manuscript for important intellectual content.  parameters. P values in bold are considered to be signi cant. Abbreviations: WBC, white blood cell; HB, hemoglobin; CRP, C-reactive protein; PCT, procalcitonin. Figure 1 Changes of body temperature and laboratory parameters in the peri-hospitalization period. Box plot with the mean line and 95% CI of the body temperature observations showing comparisons between COVID-19 and in uenza A infected children before hospital admission (A) and after 3-day of hospital stay (B). Only