**5. Conclusions**

COVID-19 might be regarded as one of the main challenges for healthcare in the twenty-first century. However, based on the ongoing collection of data, it will be possible to identify the risk group of severe COVID-19 amongst individuals with PID in the future. Patients diagnosed with PID constitute a unique population. Usually, they are provided with high-quality medical care and were well isolated throughout the pandemic. Moreover, the caregivers responsible for them are fully aware of the danger and abide by all of the hygiene standards. As a result, throughout the first wave of the pandemic, the number of infections detected in patients with PID was much smaller than in immunocompetent patients. The second and the third wave were associated with an increase in the number of infections both in adults and in children. Many of the patients managed by the department for their PID became infected at that time. However, in most cases, the disease had a mild and self-limiting course. Study results indicate that COVID-19 is not only a less severe disease in children than in adults, but also is not as severe as one might expect in children with dysfunctional immune systems. Nevertheless, this observation should not affect the sanitary regime and safety regulations concerning the management of PID patients, especially in the context of the new B.1.617.2 (delta) variant.

Remarkably, even though the most prevalent form of PID in the study group was IgG deficiency, the patients were able to respond satisfactorily to the infection in terms of anti-SARS-CoV-2 IgG. Thus, some of PID may be a group with a significance in limitation of transmission of SARS-CoV-2 viral infection after COVID-19 vaccination. According to Polish consensus by group of experts, vaccination against COVID-19 should be recommended [27].

It seems that the main factor influencing the course of COVID-19 in both immunocompetent patients and the patients with PID is comorbidity.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/jcm10215111/s1, Table S1: Clinical characteristics of patients with PID with confirmed or suspected SARS-CoV-2 infection.

**Author Contributions:** Conceptualization, K.P.-S. and A.L.-U.; Data curation, K.P.- ´ S.; Formal analysis, ´ K.S.; Investigation, K.P.- ´ S., A.K. and J.S.; Methodology, K.P.- ´ S., K. ´ S. and A.L.-U.; Project adminis- ´ tration, K.P.-S.; Supervision, A.L.-U.; Visualization, K. ´ S.; Writing—original draft, K.P.- ´ S., J.S. and ´ A.L.-U.; Writing—review & editing, K.P.-S., A.K. and A.L.-U. All authors have read and agreed to the ´ published version of the manuscript.

**Funding:** Funding within the grant A240.210.084 by Wroclaw Medical University.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board (or Ethics Committee) of Wroclaw Medical University (protocol code 472/2021; date of approval 28 May 2021).

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.

**Acknowledgments:** The authors would like to thank Przemyslaw Poltorak for linguistic help during manuscript writing.

**Conflicts of Interest:** The authors declare no conflict of interest.
