An Overview of COVID-19 and Its Vaccines

Coronavirus pandemic, is a continuing catastrophe (COVID-19) triggered by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). The virus passes into the target cells by attaching itself to a receptor i.e., Human Angiotensin-converting enzyme 2 (hACE2). It consists of Spike structures created from glycoproteins that promote the virus entry into the target cells of host. The RBD of the S1 subunit on Spike proteins binds to the hACE2 receptor, which is mostly found in the lungs, particularly type-2 pneumocytes, causing human ACE2 receptors to be downregulated. Apart from nausea, vomiting, and chest tightness, which are unusual symptoms of COVID-19, the most common causes of death and severity are respiratory failure (69.5%), sepsis or multi-organ failure (28%), cardiac failure (14.6%), and renal failure (14.6%). Viral antigen-based or viral nucleic acid-based real-time RT-PCR is recommended for the diagnosis of COVID-19 suspects. Vaccination is essential for antiviral treatment. The study was conducted on viruses based on live-attenuated or non-activated viruses, recombinant viral vectors, DNA, VLPs and soluble proteins. Vaccine from Pfizer and BioNTech was the first that showed promising data on effectiveness. 90% efficacy of the vaccine was reported. BNT-162b2 (Pfizer, BioNTech) & mRNA-1273 (Moderna) are mRNA based; AZD-1222 Ad5‑CoV (AstraZeneca; Oxford University); Ad26.COV2.S (Johnson & Johnson) are viral vector based and other vaccines have been granted emergency use authorization by FDA. Since RNA viruses are able to mutate readily and quickly the mutation in the existing strain can be Variants of concern (VOCs) that might diminish vaccine effectiveness. The latest Delta variant (B.1.671.2) has rapidly spread in India is emerging in the United States in mid-2021. It turns out to be the chief which is 6–8 fold more resistant to neutralization by sera from COVID-19 convalescent and mRNA vaccinated individuals.