COVID-19: An overview and a clinical update

Table 1 Classification of clinical types of coronavirus disease-2019 patients

Clinical types	Symptoms/clinical markers
Asymptomatic	Individuals who test positive for SARS-CoV-2 by COVID-19 nucleic acid test. Without any clinical symptoms and signs, and chest imaging is normal.
Mild	Presence of various signs and symptoms of COVID-19 (e.g., fever, fatigue, myalgia, cough, headache, sore throat, runny nose, sneezing), or digestive symptoms (nausea, vomiting, abdominal pain, diarrhea) without shortness of breath or abnormal chest imaging.
Moderate	Presence of pneumonia (frequent fever, cough) with no obvious hypoxemia (SpO2 ≥ 94% on room air at sea level); chest CT with lesions.
Severe	Patients with respiratory frequency > 30 breaths/minute; pneumonia with hypoxemia (SpO2 < 94%)on room air at sea level; a ratio of the arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) < 300 mmHg or lung infiltrates > 50%.
Critical	Acute respiratory distress syndrome may have shock, encephalopathy, myocardial injury, heart failure, coagulation dysfunction, acute kidney injury, and/or multiple organ dysfunctions.

SARS-CoV-2: Severe acute respiratory syndrome -coronavirus -2; COVID-19: coronavirus disease-2019; CT: Computed tomography; SpO_2: Saturation of oxygen; FiO_2: Forced inspiratory oxygen.

Table 2 Summary of potential treatment agents and mechanisms of action for coronavirus disease-2019 infections

Potential treatment agents	Mechanism of action
Corticosteroid	Anti-inflammatory effect
Remdesivirand ribavirin	Inhibition of the RNA-dependent RNA polymerase
Interferon therapy	Inhibition of viral entry, transcription, replication, translation, assembly
Proteaseinhibitors (lopinavir/ritonavir)	Inhibition of papain-like protease and 3C-like protease
Hydroxychloroquine and chloroquine	Inhibition of endosomal acidification and negatively influences virus–receptor binding, as well as interfere with the glycosylation of cellular receptors of SARS-CoV
Oseltamivir	Neuraminidase inhibitor
Tocilizumab	A recombinant monoclonal antibody that competitively inhibits the binding of IL-6 to its receptor.
Convalescent plasma	Neutralizing the SARS-CoV-2 antibodies

RNA: Ribonucleic acid; IL-6: Interleukin-6; SARS-CoV: Severe acute respiratory syndrome-coronavirus.

Table 3 Major COVID-19 vaccines in the pipeline

Vaccines types	Candidate vaccine
Whole virus vaccines	Adenovirus-vectored vaccine
	Live-attenuated vaccine
Nucleic acid vaccines	mRNA vaccine
	DNA vaccine
Subunit vaccines	Oral recombinant protein vaccine
	Coronavirus RBD protein-based vaccine
	Protein-based vaccine
	S-trimer recombinant protein

mRNA: Messenger ribonucleic acid; DNA: Deoxyribonucleic acid; RBD: Receptor-binding domain; S: Spike.