SARS-CoV-2

Coronavirus disease (COVID-19) is an infectious disease caused by a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that initially started in Wuhan province in China and being highly transmissible that has affected more than 200 countries worldwide and declared a Pandemic.

Coronaviruses are a group of enveloped viruses, having a positive single-stranded RNA genome and pathogenic. By metagenomic RNA sequencing and virus isolation from bronchoalveolar lavage fluid samples from patients with severe pneumonia, scientists identified that the causative agent of this emerging disease is a beta-coronavirus that had never been seen before. COVID-19 is caused by the SARS-CoV-2 is a more pathogenic form in comparison to previously identified SARS-CoV (2002) and Middle East respiratory syndrome coronavirus (MERS-CoV, 2013).

Diagnostics for SARS-CoV-2

Early diagnosis is crucial for controlling the spread of SARS-CoV-2. Molecular detection of SARS-CoV-2 nucleic acid is the gold standard. Although SARS-CoV-2 has been detected from a variety of respiratory sources, including throat swabs, posterior oropharyngeal saliva, nasopharyngeal swabs, sputum and bronchial fluid, the viral load is higher in lower respiratory tract samples. Accordingly, false negatives can be common when oral swabs and used, and so multiple detection methods should be adopted to confirm a COVID-19 diagnosis.

• Nucleic acid amplification tests (NAATs) are high-sensitivity, high-specificity tests for diagnosing SARS-CoV-2 infection based on reverse transcription polymerase chain reaction (RT-PCR). Transcription-mediated amplification (TMA) is another technique used interchangeably with RT-PCR. Loop-mediated isothermal amplification (LAMP) is a NAAT that utilizes an isothermal reaction that does not require the thermocycling process of RT-PCR.
• Antigen tests are immunoassays that detect the presence of a specific viral antigen. Antigen tests generally have similar specificity, but are less sensitive than most NAATs. Most are less expensive than NAATs and can provide results in minutes, making them useful in screening programs to quickly identify persons who are likely to have COVID-19.
• Antibody (or serology) tests are used to detect previous infection with SARS-CoV-2 and can aid in the diagnosis of multisystem inflammatory syndrome in children (MIS-C) and in adults (MIS-A). Antibody tests should not be used to determine if an individual is immune against reinfection. Antibody testing is being used for public health surveillance and epidemiologic purposes. Because antibody tests can have different targets on the virus, specific tests might be needed to assess for antibodies originating from past infection versus those from vaccination.
• Clinical assessments, in symptomatic patients, who may have a negative NAAT but whose clinical presentation is highly suggestive of SARS-CoV-2 and a diagnosis is required to enable medical care, a low-dose chest-computed tomography (CT) scan could be used to diagnose or rule out COVID-19 pathophysiology.

Figure 3. The currently widely used procedure for COVID-19 testing involves. a Collection of patient material and deposition of potential SARS-CoV-2 viral particles in transport medium. B Inactivation of the virus by detergent/chaotropic reagents or by heating. c RNA extraction. d, e Transfer to PCR-plate (96/384-well) format in which cDNA synthesis by RT and detection by qPCR may take place. [4]

Vaccine for SARS-CoV-2

To halt the pandemic, multiple SARS-CoV-2 vaccines have been developed and several have been allowed for emergency use and rollout worldwide. Hundreds of SARS-CoV-2 vaccine development programs have been initiated since the COVID-19 pandemic broke out, with some vaccines approved for widespread use.

• Inactivated vaccines are produced by growing SARS-CoV-2 in cell culture, usually on Vero cells, followed by chemical inactivation of the virus. These vaccines are usually administered intramuscularly and can contain alum (aluminium hydroxide) or other adjuvants. Because the whole virus is presented to the immune system, immune responses are likely to target not only the spike protein of SARS-CoV-2 but also the matrix, envelope and nucleoprotein.
• Live attenuated vaccines are produced by generating a genetically weakened version of the virus that replicates to a limited extent, causing no disease but inducing immune responses that are similar to that induced by natural infection. Attenuation can be achieved by adapting the virus to unfavorable conditions or by rational modification of the virus. An important advantage of these vaccines is that they can be given intranasally, after which they induce mucosal immune responses that can protect the upper respiratory tract.
• Recombinant protein vaccines can be divided into recombinant spike-protein-based vaccines, recombinant RBD-based vaccine and virus-like particle (VLP)-based vaccines. These recombinant proteins can be expressed in different expression systems including insect cells, mammalian cells, yeast and plants.
• DNA vaccines are based on plasmid DNA that can be produced at large scale in bacteria. Typically, these plasmids contain mammalian expression promoters and the gene that encodes the spike protein, which is expressed in the vaccinated individual upon delivery. The great advantage of these technologies is the possibility of large-scale production in E. coli, as well as the high stability of plasmid DNA. However, DNA vaccines often show low immunogenicity, and have to be administered via delivery devices to make them efficient.
• RNA vaccines are a relatively recent development. Similar to DNA vaccines, the genetic information for the antigen is delivered instead of the antigen itself, and the antigen is then expressed in the cells of the vaccinated individual. Either mRNA (with modifications) or a self-replicating RNA can be used. Higher doses are required for mRNA than for self-replicating RNA, which amplifies itself, and the RNA is usually delivered via lipid nanoparticles (LNPs).

SARS-CoV-2 is the third highly pathogenic human coronavirus disease to date, the rapid spreading of this highly contagious disease has posed the severest threat to global health in this century. Tackling this epidemic is a long-term job which requires efforts of every individual.