Section: Science

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According to the passage, vaccinations cannot yet work against all types of viruses because:

1. The immune system is unable to recognize proteins on the surface of the virus because they keep changing as the virus mutates, so a vaccine developed one year might not work the next.
2. The immune system is able to recognize proteins on the surface of the virus even though they keep changing as the virus mutates.
3. Vaccinations prevent the virus from mutating.
4. Mutations are caused when the virus interacts with bacteria.