This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
You have given ViPS vaccine to a person. How often will you ask him to take booster doses? 
Select and explain. 
A. Every year, B. Every 2 year, C. Every 3 year, D. Every 4 year
C: Every 3 year
Answer: C: Every 3 year 
Explanation: The injectable typhoid vaccine ViPS is a single dose vaccine which requires booster doses every 3 year. Ty21a vaccine is the oral typhoid vaccine. 3 doses are taken on day 1,3 and 5. It is effective for up to 7 years after last dose. It is recommended in people travelling to endemic areas and during out breaks. Ref: Park, Edition 21, Page - 215