Question

Given below are two statements – one is labelled as Assertion (A) and the other is labelled as Reason (R): 
Assertion (A): Human adeno-associated virus is used to deliver single-stranded DNA as a vaccine that does not require multiple booster doses.
Reason (R): Such vaccines are generally administered along with an adenovirus or a herpesvirus to avoid multiple booster doses. 
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both A and R are correct and R is the correct explanation of A.
• B. Both A and R are correct, but R is NOT the correct explanation of A.
• C. A is correct, but R is not correct.
• D. A is not correct, but R is correct.

Hint:

In assertion-reason questions, carefully examine both the factual accuracy and the causal relationship. A correct explanation must directly address the mechanism or reasoning behind the assertion.

Answer 1

The Correct Option is A

Step 1: Understand Assertion (A)
Adeno-associated viruses (AAVs) are commonly used vectors in gene therapy and vaccine platforms. 
AAVs deliver single-stranded DNA (ssDNA) into host cells. 
These vectors are non-pathogenic and have low immunogenicity. 
AAV-based vaccines can generate long-lasting immune responses, thereby reducing the need for multiple booster doses. 
Hence, Assertion (A) is correct. 
Step 2: Understand Reason (R)
AAVs often require the presence of helper viruses like adenovirus or herpesvirus to complete their life cycle and enhance the transgene expression. 
These helper viruses provide essential helper functions (e.g., transcriptional activation, replication enzymes) that increase the efficiency of AAV transduction. 
By enhancing gene expression, they also enhance the immune response, potentially eliminating the need for additional booster doses. 
Hence, Reason (R) is also correct. 
Step 3: Relationship between A and R
The co-administration of adenovirus or herpesvirus is a critical helper mechanism that boosts the effectiveness of AAV-based vectors. 
This mechanistic help is exactly why AAV-based vaccines often do not require boosters. 
Therefore, R correctly explains A.