Background Evidence suggests that the outbreak of the coronavirus disease 2019 (COVID-19) and the prevention/control measures for COVID-19 may cause insomnia during the acute phase of COVID-19 pandemic in China. However, it is unclear whether insomnia sustains during the later phases of the pandemic. Methods We searched PubMed/Medline, EMBASE, PsycINFO and China National Knowledge Infrastructure from the 27 th December 2019 to the 2 nd February 2021. As early stage studies on COVID-19 pandemic in China were defined as those conducted prior to April 1 st , 2020, while late stage studies were those conducted after April 1 st , 2020. Results A total of 98 studies with 193,889 participants were included. The pooled prevalence of insomnia symptoms among all populations was 39.1%; the pooled prevalence of insomnia symptoms during the early and late stages of COVID-19 in China were 37.0% (95% CI 34.1-39.9%) and 41.8% (95% CI 33.6-50.0%), respectively. Importantly, there was no significant difference regarding the prevalence of insomnia symptoms between the early and late stages of COVID-19. Meta-regression showed that healthcare workers, COVID-19 patients, patients with chronic medical conditions and patients with mental disorders had a higher prevalence of insomnia symptoms compared to the general population. This association remained significant in healthcare workers and patients with chronic medical conditions after adjusting for age, gender, areas of high or low prevalence of COVID-19 cases, anxiety and depression. Conclusions Over one third of our sample presented insomnia symptoms during the early stage of COVID-19 pandemic in China. Interestingly, prevalence of insomnia symptoms sustained high during the late stage of the pandemic despite the control of the disease and the amelioration of its adverse effects. Our findings suggest that insomnia symptoms related to COVID-19 appear to persist of over time.

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Prion diseases are fatal neurodegenerative processes caused by the accumulation of the pathological prion protein, PrPSc. While pathological lesions are limited to the central nervous system (CNS), disease‐specific proteins accumulate and replicate in secondary lymphoid organs prior to neuroinvasion, and their replication there depends on the abundance of cellular prion protein (PrPC). PrPC is expressed in both central and peripheral lymphoid tissues, and up‐ or downregulates innate and adaptive immune responses. In addition to prion diseases, PrPC is also immunologically involved in other neurological disorders and infectious diseases, including Alzheimer's disease and human immunodeficiency virus infection. Herein, we summarize the expression and functions of PrPC in various immunocytes, as well as its immunological and pathological roles in neurodegeneration and infection.