Question

Covishield is a vaccine used to create immunological memory against COVID infection. It is made by inserting gene encoding covid spike protein to the adenovirus vector, which when injected to the human body releases the gene in human cells and hence produces spike proteins. Yet it is not able to replicate itself because:

• A. The adenovirus only grows in bacterial population
• B. Genes involved in growth and proliferation have been replaced by spike protein encoding genes.
• C. Adenovirus has been attenuated and hence its growth is inhibited.
• D. Killed Adenovirus is injected into the human body.

Answer 1

Answer: (B)

Genes involved in growth and proliferation have been replaced by spike protein encoding genes.

Answer 2

Covishield is an adenovirus-vectored vaccine. For safety and to prevent the vaccine from causing disease, the adenovirus vector is engineered to be replication-deficient. This is achieved by removing or replacing essential viral genes required for the virus to replicate its genome and produce new viral particles. In the case of Covishield, the gene encoding the COVID spike protein is inserted into the adenovirus genome, replacing genes vital for viral replication (e.g., the E1 gene). This modification allows the adenovirus to enter human cells and deliver the spike protein gene, leading to the production of spike proteins and the induction of an immune response, but it prevents the virus from multiplying and spreading within the body.

Let's evaluate the given options:

• (A) The adenovirus only grows in bacterial population: This is incorrect. Adenoviruses are viruses that infect eukaryotic cells (like human cells), not bacteria.
• (B) Genes involved in growth and proliferation have been replaced by spike protein encoding genes: This is the correct explanation. Essential viral genes (like E1) required for the adenovirus to replicate are deleted and replaced by the gene encoding the SARS-CoV-2 spike protein. This makes the vector replication-incompetent.
• (C) Adenovirus has been attenuated and hence its growth is inhibited: While attenuation weakens a pathogen, making it less virulent, it usually still involves some level of replication. For viral vectors like in Covishield, the aim is typically complete replication deficiency, which is more accurately described by the replacement of essential genes rather than just attenuation.
• (D) Killed Adenovirus is injected into the human body: This is incorrect. Covishield uses a live (though replication-deficient) viral vector to deliver the gene. A "killed" virus would not be able to deliver its genetic material and express the spike protein effectively.

Therefore, the adenovirus vector used in Covishield cannot replicate because its essential replication genes have been removed and replaced by the spike protein gene.