SARS-CoV-2 infection in pediatric population before and during the Delta (B.1.617.2) and Omicron (B.1.1.529) variants era

(2022) 19:144 Khemiri et al. Virology Journal https://doi.org/10.1186/s12985-022-01873-4 Open Access REVIEW SARS‑CoV‑2 infection in pediatric population before and during the Delta (B.1.617.2) and Omicron (B.1.1.529) variants era Haifa Khemiri1,2, Kaouther Ayouni1,2, Henda Triki1 and Sondes Haddad‑Boubaker1,2* Abstract Background: COVID-19, the coronavirus disease that emerged in December 2019, caused drastic damage world‑ wide. At the beginning of the pandemic, available data suggested that the infection occurs more frequently in adults than in infants. In this review, we aim to provide an overview of SARS-CoV-2 infection in children before and after B.1.617.2 Delta and B.1.1.529 Omicron variants emergence in terms of prevalence, transmission dynamics, clinical manifestations, complications and risk factors. Methods: Our method is based on the literature search on PubMed, Science Direct and Google Scholar. From Janu‑ ary 2020 to July 2022, a total of 229 references, relevant for the purpose of this review, were considered. Results: The incidence of SARS-CoV-2 infection in infants was underestimated. Up to the first half of May, most of the infected children presented asymptomatic or mild manifestations. The prevalence of COVID-19 varied from country to another: the highest was reported in the United States (22.5%). COVID-19 can progress and become more severe, especially with the presence of underlying health conditions. It can also progress into Kawasaki or Multisystem Inflam‑ matory Syndrome (MIS) manifestations, as a consequence of exacerbating immune response. With the emergence of the B.1.617.2 Delta and B.1.1.529 Omicron variants, it seems that these variants affect a large proportion of the younger population with the appearance of clinical manifestations similar to those presented by adults with impor‑ tant hospitalization rates. Conclusion: The pediatric population constitutes a vulnerable group that requires particular attention, especially with the emergence of more virulent variants. The increase of symptomatic SARS-CoV-2 infection and hospitalization rate among children highlights the need to extend vaccination to the pediatric population. Keywords: Children, Delta variant, Omicron variant, Symptoms, COVID-19, Prevalence, MIS-C, Immunodepressive, Risk factors Introduction Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19), has spread rapidly around the world *Correspondence: 1 Laboratory of Clinical Virology, WHO Regional Reference Laboratory for Poliomyelitis and Measles for the EMR, Institut Pasteur de Tunis, University of Tunis El Manar, 13 place Pasteur, BP74 1002 le Belvédère, Tunis, Tunisia Full list of author information is available at the end of the article since its emergence in Wuhan, China, late 2019 [1, 2]. By January 2020, the virus has been isolated and sequenced [3, 4], revealing close relationships to coronaviruses such as SARS-CoV [5] and MERS-CoV [6]. On March 11, 2020, the World Health Organization (WHO) announced COVID-19 as a pandemic [7] causing 430,257,564 confirmed cases of COVID-19, including 5,922,047 deaths up to 25 February 2022 [8]. SARS-CoV-2 is an enveloped, positive RNA virus [9]. It belongs to the family of Coronaviridae, the subfamily © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativeco mmons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Khemiri et al. Virology Journal (2022) 19:144 Page 2 of 16 of Orthocoronavirinae, the genera of Betacoronavirus and subgenus of Sarbecovirus [10, 11]. It is responsible for severe lower respiratory tract infections in humans [12]. SARS-CoV-2 causes pneumonia, characterized by fever, cough, shortness of breath, and bilateral infiltration on chest imaging [2, 12]. It can also induce fatal lung damage, multiple organ failure and death [9, 13]. The clinical manifestations can be classified into four severity of illness categories: asymptomatic, mild, moderate and severe clinical [14]. In contrast with adults who can develop the four types of clinical manifestations, children are mainly asymptomatic or present mild infection and, in some cases, they can develop severe post-COVID-19 manifestations such as Kawasaki-like symptoms [15–18]. After a year into the COVID-19 pandemic, new variants emerged and spread rapidly across the continents [19]. In the United Kingdom, the B.1.617.2 Delta variant, initially identified in India in October 2020, spreads rapidly through schools [20]. Children seem to be the most affected category [19, 21, 22]. The B.1.1.529 Omicron variant first detected in South Africa, in 2021, appeared to be more contagious than the Delta variant, associated with a significant increase in the number of pediatric and adults SARS-CoV-2 infections [23–28]. This review gives an overview of SARS-CoV-2 infection in children before and after B.1.617.2 Delta and B.1.1.529 Omicron variants emergence. We analyzed current knowledge on the prevalence, clinical manifestations and complications among immunocompetent and immunodepressive children as well as risk factors for the severity of COVID-19. Methods Original research studies published on COVID-19/ SARS-CoV-2 among children in English, between January 2020 and July 2022, were identified using PubMed, Science Direct and Google Scholar. The search used combinations of the keywords “COVID-19,” “SARS-CoV-2,” “clinical manifestations” “prevalence”, “Transmission”, “pediatric population,” “child”, “SARS-CoV-2 variants”, “Delta variant”, ”B.1.617.2”, “Omicron variant”, “B.1.1.529”, “Risk factors” and “COVID-19 vaccines” (Fig. 1). In addition, the reference lists of the retrieved articles were checked for other relevant articles. Moreover, 229 references were considered relevant to the aim of this review. An additional table file shows more details about these references (see Additional file 1: Table S1). Epidemiology of COVID‑19 in infants and children Epidemiology of COVID‑19 in infants before the Del (...truncated)