A point mutation arises in the active site of an RNA virus protease, lowering affinity for a widely used protease inhibitor but also reducing catalytic efficiency by 40%. What is the most likely net effect on viral population fitness and drug sensitivity in patients?

• A. No change in clinical outcome because protease inhibitors never affect viral replication dynamics, so mutations in protease have no impact on drug sensitivity or fitness.
• B. Immediate elimination of the virus by host immunity, because mutations in protease active sites universally expose viral epitopes to antibodies that clear infection within hours.
• C. Partial drug resistance may emerge because inhibitor binding is reduced, but viral fitness will be compromised due to less efficient polyprotein cleavage, potentially limiting spread compared to wild-type virus.
• D. Complete restoration of viral fitness because any mutation that reduces inhibitor binding always produces compensatory increases in replication speed and overall infectivity.

Answer: (C)