Fighting disease with disease

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Across
  1. 3. spread to everyone
  2. 6. away doing things
  3. 8. treat
  4. 10. injection
  5. 11. 100 years
Down
  1. 1. not proven idea
  2. 2. fight/protect
  3. 3. time/period
  4. 4. bacteria
  5. 5. hard/difficult
  6. 7. illness
  7. 9. something that make you sick