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Year and pandemic name |
1918 (H1N1), 1957 (H2N2), 1968 (H3N2), 2009 (H1N1), and Flu pandemics |
2019 and COVID-19 |
Virus family |
Orthomyxoviridae |
Coronaviridae (genus β-CoVs) |
Structure |
An enveloped, negative-sense, and single-stranded RNA virus; slightly ovoid or mostly round; diameter of 80–120 nm |
An enveloped, positive-sense, and single-stranded RNA virus; spherical or round in shape; diameter of 60–140 nm |
Genome size |
13.5 kb |
29.9 kb |
Mode of transmission |
Droplet, aerosol, direct contact, and fecal–oral route |
Droplet, aerosol, direct contact, and fecal–oral route |
Replication sites |
Upper respiratory tract and, in severe cases, lower respiratory tract |
Starts from the upper respiratory tract, infects the lower respiratory tract, and spreads to other organs (cardiovascular, intestinal, kidney, and nervous system) |
Incubation period |
1–7 days |
2–14 days (a maximum of 24 days) |
Host receptor and entry |
Terminal glycosides of sialic acid |
ACE2 and TMPRSS2 |
Cellular tropism |
Epithelial cells of Respiratory tract: Alveolar Epithelial cells and ciliated cells |
Epithelial cells of the respiratory tract: alveolar epithelial cells, ciliated cells, basal cells of the olfactory epithelium, intestinal epithelial cells, renal parenchymal cells, and endothelial cells |
Viral protein binding to host receptor |
HA |
Spike (S) protein |
Replication |
Nuclear |
Cytoplasm |
Symptom |
Fever, dry cough, sore throat, fatigue, and nasal congestion |
High fever, dry cough, fatigue, ARDS, and anosmia |
Extrapulmonary complications |
In rare cases, myocarditis and encephalitis |
In most cases, anosmia, thrombosis, stroke, encephalitis, and diarrhea |
Target for neutralizing antibodies |
HA and NA |
RBD of the spike protein |
Hematological parameters |
Lymphopenia and CRP ↑ |
Type I interferon ↓, neutrophil counts ↑, and significant lymphopenia |
Variants of concern (VOCs) |
1957 H2N2, 1968 H3N2, and 2009 H1N1 |
Alpha, Beta, Gamma, Delta, and Omicron |
Mortality rate |
0.05–0.1% (seasonal influenza) |
~1–3.4% (higher in early wave) |
Vaccine availability |
Annual seasonal vaccines (inactivated, live) |
Multiple vaccines (mRNA, vector-based, inactivated) |
Mutations/variants |
Antigenic shift and drift |
Frequent mutations with variants of concern (e.g., Delta and Omicron) |
Treatment options |
Antivirals (e.g., oseltamivir and zanamivir) |
Antivirals (e.g., remdesivir, molnupiravir, and Paxlovid), mAbs |
Complications |
Pneumonia and secondary bacterial infections |
Pneumonia, acute respiratory distress syndrome (ARDS), and multi-organ damage |
References |
[26,27] |
[28,29] |