Step 1: Name the two polio vaccines side by side.
There are two vaccines used against polio: an injected, inactivated vaccine developed by Jonas Salk, and an oral, weakened live vaccine developed later by Albert Sabin.
Step 2: Match each name to its common alternate name.
The injectable inactivated version is commonly called Salk's vaccine, after its developer, while the oral drop version is called Sabin's vaccine.
Step 3: Confirm which one the question is naming.
Since the question asks what the polio vaccine is "also called", and the well known alternate name tied to polio in this context is Salk's vaccine, that is the match.
Step 4: Clear out the unrelated options.
BCG protects against tuberculosis, DPT protects against diphtheria, pertussis and tetanus together, and HPP is not a recognized vaccine name at all. None of these are alternate names for the polio vaccine.
Final Answer:
The polio vaccine is also called Salk's vaccine, option (3).