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SPICES, School of Medical Sciences  |  Health Campus, USM

Covid 19

covid 19

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2)

SARS-CoV-2 is the causative of Covid-19, a respiratory infection which first emerged in late 2019 in China. The novel virus belongs to the Coronaviridae family, a group of enveloped, positive-stranded RNA viruses.  SARS-CoV-2 infects humans, birds and other mammals. Corona means crown in Greek and hence, the name is given because the glycoprotein surrounding the virion gives a crown appearance when observed on electron microscopy. 

Coronaviruses have four genera: α-, β-, δ-, and γ-coronavirus. SARS-CoV-2 together with severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) belong to the lineage B of the genus β-coronavirus.  

SARS-CoV-2 has a large genome, with a size of 26-32kb. Within the genome, there are six functional open reading frames (ORFs): replicase (ORF1a/ORF1b), spike (S), envelope (E), membrane (M) and nucleocapsid (N). 

There are several diagnostic methods available for the detection of SARS-CoV-2, the virus that causes COVID-19. These methods can be broadly classified into two categories: molecular tests and protein-based (Antigen/ Antibody) or serological tests.

  1. Molecular tests: 
  • Reverse Transcription Polymerase Chain Reaction (RT-PCR): This is the most commonly used method for SARS-CoV-2 detection. It detects the viral RNA in a patient's sample (typically obtained from nasal or throat swabs) and amplifies it using reverse transcription followed by polymerase chain reaction (PCR). RT-PCR can provide highly sensitive and specific results.
  • Isothermal Nucleic Acid Amplification Tests (NAATs): These tests, such as loop-mediated isothermal amplification (LAMP) and nucleic acid sequence-based amplification (NASBA), can also detect viral RNA but do not require the temperature cycling involved in PCR. They are often simpler, faster, and more suitable for point-of-care testing.
  • CRISPR-based Tests: Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technology has been adapted for SARS-CoV-2 detection. It utilizes the Cas enzyme to detect and amplify viral genetic material, providing a rapid and specific diagnostic method.
  1. Protein-based (Antigen/ Antibody) or serological tests
  • Rapid Antigen Tests: These tests detect specific viral proteins (antigens) in respiratory samples. They are relatively quick and can provide results within minutes. Rapid antigen tests are less sensitive than molecular tests but can be useful for rapid screening in certain settings, such as point-of-care or community testing.
  • Antibody Tests: These tests detect the presence of antibodies produced by the immune system in response to SARS-CoV-2 infection. They are performed on blood samples and can help determine if a person has been previously exposed to the virus. Antibody tests are unsuitable for early-stage diagnosis as it takes time for the body to produce detectable levels of antibodies.

Vaccination is a crucial tool in the fight against SARS-CoV-2 and the prevention of COVID-19. Several vaccines have been developed and authorized for emergency use or approved for full use in different countries. 

Vaccine Types:

  1. mRNA Vaccines: These vaccines, such as the Pfizer-BioNTech and Moderna vaccines, use messenger RNA (mRNA) to deliver instructions to cells to produce a harmless piece of the viral spike protein. This protein triggers an immune response, training the immune system to recognize and fight the virus.
  2. Viral Vector Vaccines: Vaccines like the Oxford-AstraZeneca and Johnson & Johnson vaccines use a modified adenovirus (common cold virus) to deliver a piece of the SARS-CoV-2 genetic material into cells. This also prompts an immune response.
  3. Protein Subunit Vaccines: These vaccines, such as the Novavax vaccine, contain harmless pieces (subunits) of the SARS-CoV-2 spike protein. They stimulate an immune response when injected.
  4. Inactivated virus vaccine: The Sinopharm vaccine, also known as BBIBP-CorV, is an inactivated virus vaccine. It uses a traditional method where the SARS-CoV-2 virus is inactivated or killed before being used in the vaccine. The inactivated virus cannot replicate or cause disease but can still stimulate an immune response.

Vaccine Effectiveness:

In clinical trials, COVID-19 vaccines have demonstrated high efficacy in preventing symptomatic COVID-19 and severe disease. They have also shown effectiveness against various SARS-CoV-2 variants.

While breakthrough infections (infections in fully vaccinated individuals) can occur, vaccinated individuals are generally less likely to develop severe illness or require hospitalization if infected.

Vaccine Distribution and Administration:

COVID-19 vaccines are typically administered via intramuscular injection, often requiring two doses for full vaccination. The specific dosing regimen varies depending on the vaccine brand.

Governments and health organizations have implemented vaccination campaigns to prioritize high-risk populations, such as healthcare workers, elderly individuals, and those with underlying health conditions. Many countries have expanded vaccine availability to the general population.

Vaccine Safety:

COVID-19 vaccines undergo rigorous testing in clinical trials to assess safety and efficacy. They are authorized or approved for use by regulatory authorities based on a thorough review of trial data.

Common side effects of COVID-19 vaccination include pain at the injection site, fatigue, headache, muscle pain, and fever. Serious side effects are rare.

Importance of Vaccination:

Vaccination is critical in reducing the spread of SARS-CoV-2, protecting individuals from severe illness, and helping to achieve herd immunity.

Herd immunity occurs when a significant portion of the population is immune to the virus, either through vaccination or previous infection, reducing the overall virus transmission and protecting vulnerable populations.

It's important to follow local health guidelines and consult healthcare professionals for accurate and up-to-date information on COVID-19 vaccination, including eligibility, scheduling, and any specific recommendations based on individual health conditions or circumstances.