Question:
Covishield is a vaccine used to create immunological memory against COVID-19 infection. It is made by inserting the gene coding for the SARS-CoV-2 spike protein into an adenovirus vector. When injected into the human body, the vector releases the gene into human cells, which then produce the spike protein. However, the adenovirus vector is not able to replicate itself because:
Covishield is a vaccine used to create immunological memory against COVID-19 infection. It is made by inserting the gene coding for the SARS-CoV-2 spike protein into an adenovirus vector. When injected into the human body, the vector releases the gene into human cells, which then produce the spike protein. However, the adenovirus vector is not able to replicate itself because:
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Covishield is a viral vector vaccine. The adenovirus used as a vector is genetically engineered to be replication-deficient by deleting essential replication genes and inserting the SARS-CoV-2 spike protein gene.
Updated On: Jun 11, 2026
- The adenovirus only grows in bacterial populations.
- Genes involved in growth and replication have been replaced by the spike protein coding gene.
- The adenovirus has been attenuated; hence its growth is inhibited.
- A killed adenovirus is injected into the human body.
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The Correct Option is B
Solution and Explanation
Concept:
Covishield is a viral vector vaccine. It uses a genetically modified adenovirus as a carrier (vector) to deliver the gene encoding the SARS-CoV-2 spike protein into human cells.
The purpose of the vector is only to transport the genetic information. After entering the host cells, the spike protein is produced, which stimulates the immune system to generate antibodies and immunological memory.
To ensure safety, the adenovirus vector is engineered so that it cannot replicate inside human cells.
Step 1: Understand the structure of the vaccine. Covishield uses a modified chimpanzee adenovirus vector. Scientists insert the gene coding for the coronavirus spike protein into the adenoviral genome. The modified virus acts as a delivery vehicle for the spike protein gene.
Step 2: Why can the adenovirus not replicate? For a virus to replicate, it must possess genes required for:
• Viral DNA replication
• Viral protein synthesis
• Assembly of new viral particles
During vaccine development, important adenoviral genes responsible for replication are removed or inactivated. The spike protein gene is inserted in place of these deleted regions. As a result: Replication genes are absent and therefore the vector cannot produce new virus particles. This makes the vaccine much safer because the vector can infect cells and express the spike protein but cannot multiply.
Step 3: Examine Option (A). ``The adenovirus only grows in bacterial populations'' This is incorrect. Adenoviruses infect animal cells, not bacteria. Therefore Option (A) is false.
Step 4: Examine Option (B). ``Genes involved in growth and replication have been replaced by the spike protein coding gene'' This accurately describes the design of replication-deficient adenoviral vectors. Therefore Option (B) is correct.
Step 5: Examine Option (C). Attenuation means weakening a pathogen. Although some vaccines use attenuated organisms, Covishield specifically employs a replication-deficient viral vector created through genetic modification. The inability to replicate is due to deletion of replication genes rather than simple attenuation. Therefore Option (C) is incorrect.
Step 6: Examine Option (D). A killed virus vaccine contains inactivated virus particles. Covishield is not an inactivated adenovirus vaccine. It uses a live but replication-deficient viral vector. Therefore Option (D) is incorrect.
Step 7: Final conclusion. The adenovirus vector cannot replicate because genes necessary for viral replication have been removed and replaced with the spike protein coding sequence. Hence the correct answer is \[ \boxed{\text{(B) Genes involved in growth and replication have been replaced by the spike protein coding gene.}} \]
Step 1: Understand the structure of the vaccine. Covishield uses a modified chimpanzee adenovirus vector. Scientists insert the gene coding for the coronavirus spike protein into the adenoviral genome. The modified virus acts as a delivery vehicle for the spike protein gene.
Step 2: Why can the adenovirus not replicate? For a virus to replicate, it must possess genes required for:
• Viral DNA replication
• Viral protein synthesis
• Assembly of new viral particles
During vaccine development, important adenoviral genes responsible for replication are removed or inactivated. The spike protein gene is inserted in place of these deleted regions. As a result: Replication genes are absent and therefore the vector cannot produce new virus particles. This makes the vaccine much safer because the vector can infect cells and express the spike protein but cannot multiply.
Step 3: Examine Option (A). ``The adenovirus only grows in bacterial populations'' This is incorrect. Adenoviruses infect animal cells, not bacteria. Therefore Option (A) is false.
Step 4: Examine Option (B). ``Genes involved in growth and replication have been replaced by the spike protein coding gene'' This accurately describes the design of replication-deficient adenoviral vectors. Therefore Option (B) is correct.
Step 5: Examine Option (C). Attenuation means weakening a pathogen. Although some vaccines use attenuated organisms, Covishield specifically employs a replication-deficient viral vector created through genetic modification. The inability to replicate is due to deletion of replication genes rather than simple attenuation. Therefore Option (C) is incorrect.
Step 6: Examine Option (D). A killed virus vaccine contains inactivated virus particles. Covishield is not an inactivated adenovirus vaccine. It uses a live but replication-deficient viral vector. Therefore Option (D) is incorrect.
Step 7: Final conclusion. The adenovirus vector cannot replicate because genes necessary for viral replication have been removed and replaced with the spike protein coding sequence. Hence the correct answer is \[ \boxed{\text{(B) Genes involved in growth and replication have been replaced by the spike protein coding gene.}} \]
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