*Article* **Assessment of COVID-19 Incidence and the Ability to Synthesise Anti-SARS-CoV-2 Antibodies of Paediatric Patients with Primary Immunodeficiency**

**Karolina Pieniawska-Smiech ´ 1,2,\*, Anna Kuraszewicz 2, Joanna Sado 2, Karol Smiech ´ <sup>3</sup> and Aleksandra Lewandowicz-Uszy ´nska 2,4,\***


**Abstract:** Background: Data regarding the course of SARS-CoV-2 infection in children with primary immunodeficiency (PID) is insufficient. The purpose of the study was to evaluate the morbidity and clinical course of COVID-19 and the ability to produce anti-SARS-CoV-2 IgG antibodies in children with PID. Methods: In this retrospective study, medical records of 99 patients aged 0–18 were evaluated. The patients were divided into three groups: PID group (68.69%), control group (19.19%) and patients with ongoing or previous paediatric inflammatory multisystem syndrome (12.12%). Data such as morbidity, clinical outcome, and IgG anti-SARS-CoV-2 antibody titres were assessed. Results: A confirmed diagnosis of SARS-CoV-2 infection has been established in 26.47% of patients with PID. Among patients with PID infected with SARS-CoV-2, only three cases were hospitalised. Mortality in the PID group was 0%. Throughout an observation period of 1 year, 47.06% of patients with PID were tested positive for the anti-SARS-CoV-2 antibody. Conclusions: In the study group, in most cases the disease had a mild and self-limiting course. Remarkably, even though IgG deficiency was the most prevalent form of PID in the study group, the patients were able to respond satisfactorily to the infection in terms of anti-SARS-CoV-2 IgG.

**Keywords:** anti-SARS-CoV-2 antibodies; COVID-19; primary immunodeficiency; SARS-CoV-2; PIMS-TS

**1. Introduction**

At the end of 2019, a new strain of pneumonia-causing coronavirus was identified in Wuhan, China [1]. Its rapid spread resulted in an outbreak of an epidemic that started in China and gradually expanded worldwide [2,3]. The causative virus, initially called 2019-nCoV, was named SARS-CoV-2, and the disease associated with it–COVID-19 [4].

Primary immunodeficiency (PID) manifests mainly as recurrent and/or severe infections, and patients affected by PID constitute a unique population [5]. If possible, medical interventions should focus on correcting the immune defect in the first place. Another important goal is the prevention and treatment of infections that are still an important cause of mortality in this patient group.

The Center for Disease Control and Prevention (CDC) recognises PID as a risk factor of severe clinical course of COVID-19 [6,7]. Data regarding the course of SARS-CoV-2 infection in children, including children with PID, are insufficient. Other areas that need further research are the duration time of immunity to reinfection and the applicability of

**Citation:** Pieniawska-Smiech, K.; ´ Kuraszewicz, A.; Sado, J.; Smiech, K.; ´ Lewandowicz-Uszy ´nska, A. Assessment of COVID-19 Incidence and the Ability to Synthesise Anti-SARS-CoV-2 Antibodies of Paediatric Patients with Primary Immunodeficiency. *J. Clin. Med.* **2021**, *10*, 5111. https://doi.org/10.3390/ jcm10215111

Academic Editors: Rita Consolini and Giorgio Costagliola

Received: 3 October 2021 Accepted: 28 October 2021 Published: 30 October 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

serological methods in confirming previous infections [8–12]. Following appropriate validation, serologic tests detecting anti-SARS-CoV-2 antibodies might help identify patients who were infected with the new coronavirus in the past [13–16]. To increase the predictive value of serological methods, it has been suggested that only the tests with high specificity (>99.5%) were used only on individuals with a high clinical probability of a previous infection. The main disadvantages of serologic tests are limited use in the diagnosis of the acute phase of the infection, variable sensitivity and specificity, depending on the assay, and relatively high costs and absence of antibody synthesis in response to the infection in some patients [17]. It is obvious that such a phenomenon may be observed in patients with immune deficiency, both congenital and acquired. The purpose of the study was to evaluate the morbidity and clinical course of COVID-19 and the ability to produce the anti-SARS-CoV-2 IgG antibodies in children with PID. At the same time, the applicability of serological methods in the diagnosis of SARS-CoV-2 in this group of patients was assessed.
