**Question:** Which of the following is not true about Sabin vaccine?

A. Sabin vaccine is a live, attenuated oral polio vaccine.
B. Sabin vaccine contains three different poliovirus serotypes.
C. Sabin vaccine is effective in preventing both types 1 and 3 polio infections.
D. Sabin vaccine is less effective in preventing type 2 polio infections.

**Core Concept:** Sabin vaccine is a live, attenuated oral polio vaccine developed by Albert Sabin in the 1950s. It consists of three different poliovirus serotypes (type 1, 2, and 3) that are attenuated, meaning they have been weakened but still retain their ability to replicate within the intestine, stimulating an immune response.

**Why the Correct Answer is Right:** D is the correct answer because Sabin vaccine is less effective in preventing type 2 polio infections due to the fact that the vaccine strain used for type 2 is more attenuated, making it less likely to induce a robust immune response. This can lead to an increased risk of vaccine-associated paralytic polio (VAPP) cases, especially in children with a weakened immune system.

**Why Each Wrong Option is Incorrect:**

A is correct because Sabin vaccine is indeed a live, attenuated oral polio vaccine that stimulates an immune response in the gut.

B is correct because Sabin vaccine contains three different poliovirus serotypes (type 1, 2, and 3) that stimulate immunity against each of these serotypes.

C is incorrect as Sabin vaccine is less effective in preventing type 2 polio infections, as explained above.

**Clinical Pearl:** The use of Sabin vaccine has significantly reduced global polio cases since its introduction, leading to the declaration of Polio Eradication in 2020 by the World Health Organization (WHO). However, its limitations in type 2 prevention highlight the importance of using a different polio vaccine (IPV, Inactivated Polio Vaccine) for type 2 polio prevention in current vaccination strategies.