Dear Colleagues,

COVID-19 is a contagious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was identified in Wuhan, China, in December 2019. The disease spread worldwide, leading to an ongoing pandemic which was announced on March 11, 2020 by the World Health Organization (WHO). In the face of the growing number of patients affected by this disease, there was an urgent need to determine how to treat it and effectively detect infection. In one of the more severe stages of the pandemic, i.e., in May 2020, the highest mortality rate was observed in Italy, which was 14%.

In March 2020, scientists performed full sequencing of the new coronavirus, SARS-CoV-2, which contributed to the subsequent development of vaccines. The genome of the new coronavirus, SARS-CoV-2, shows 79% similarity to SARS-CoV-1 and 50% similarity to MERS-CoV. In addition, SARS-CoV-2, similarly to all coronaviruses, has a positive RNA strand. SARS-CoV-2 is mainly spread via droplet–air. Infection can also occur through the direct contact of mucous membranes with contaminated surfaces, e.g., through dirty hands. Infection occurs as a result of binding the SARS-CoV-2 S protein to, e.g., the ACE2 receptor, located, among other areas, on type 2 follicular epithelial cells. SARS-CoV-2 infection has a wide clinical spectrum; however, the course of the disease in most patients is mild and does not require hospitalization.

The first stage of the disease is often asymptomatic or with mild symptoms, e.g., fever, chills or cough. In some patients, especially young people, a loss of smell (anosmia) or loss of taste (ageusia) may be the only manifestation of the disease. In turn, in the elderly, the occurrence of unusual symptoms such as body temperature fluctuations, deliration and falls (associated with fatigue and weakness) may precede respiratory symptoms. After the acute phase of COVID-19, post COVID syndrome could occur (PC19, long-COVID). Its frequency, exact clinical picture and therapeutic recommendations are not yet fully known. Post COVID syndrome is assumed to include an abnormality 4 weeks after the onset of COVID-19. The most common complications are pulmonary tiredness, dyspnea, heart palpitations and olfactory and taste disturbances.

Despite the fact that on May 5, 2023, WHO declared the end of the COVID-19 global health emergency, we are still struggling with its consequences. However, during the pandemic, many studies and observations were carried out that expanded our knowledge about COVID-19. That is why this Special Issue aims to encourage continued comprehensive study in the field of biomolecular science connected with this disease over the past four years.

Dr. Monika Zajkowska
Dr. Monika Gudowska-Sawczuk
Guest Editors

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• COVID-19
• SARS-CoV-2
• pandemic
• diagnosis
• biomarkers
• treatment
• immunity
• inflammation
• cytokines
• vaccine