Explain why it is difficult to develop drugs that can be used to treat viral infections.

Eduqas GCSE Biology — 2.6.3 Medicines and drugs · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Viruses replicate only inside host cells, so a drug that destroys the virus would also harm the host cell.

Because viruses mutate rapidly, a drug that works on one strain may become ineffective when the virus changes.

Thus, targeting viruses is difficult: the drug must kill the virus without damaging the host, and it must remain effective despite rapid viral mutation.

Examiner tips

  • Use the exact phrases: "replicate inside host cells", "kill/damage the host cell", "mutate rapidly", "new strain may not be affected".
  • Show the cause–effect chain: virus inside cell → drug harms cell; mutation → drug loses efficacy.

Common mistakes

  • Confusing virus replication with bacterial replication; forgetting the host cell damage point.
  • Omitting the rapid mutation aspect or the strain‑specific issue.

Mark scheme (4 marks)

  1. Viruses live/reproduce inside host cells
  2. A drug that kills/damages the virus would also damage/kill the host cell
  3. Viruses mutate rapidly / viruses change quickly
  4. This means a drug developed against one strain may not work against a mutated/new strain

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