Section: Science

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From the information given in the passage, it can be assumed HIV has successfully avoided vaccines because:

1. its proteins are in a state of continual mutation.
2. it is not actually a virus.
3. the more contagious a virus is, the harder it is to vaccinate.
4. None of the above.

Answer 1 is correct as implied when the author explains the immune system works "by recognising the proteins on the surface of the virus. But in certain types of virus, these proteins keep changing as the virus mutates, so a vaccine developed one year might not work the next. … Viruses like HIV have proved impossible to develop any kind of vaccine for at all."