QUESTION TYPE: Paradox
FACTS: The vaccine against hepatitis is 100% effective. Yet some people in the group who received the vaccine nonetheless exhibited symptoms of hepatitis A.
The symptoms always take at least 60 days to appear.
ANALYSIS: One possible answer would be that other diseases also cause the same symptoms that hepatitis A causes.
Instead the question requires you to know something about vaccines: they prevent disease but they do not cure it. If you are already infected a vaccine can’t help you. So it could be that the people who exhibited symptoms were already infected. The symptoms take a while to show up.
- The placebo group isn’t puzzling. The strange thing is that people who actually received the vaccine still got sick.
- This shows that the vaccine group received some benefit but it doesn’t explain why there were still some sick people.
- This shouldn’t matter: the vaccine is supposed to work every time. Yet some people got sick.
- CORRECT. The vaccine can’t help you once you have the disease.
- This shows the vaccine might have helped. But it’s supposed to prevent the disease entirely. This doesn’t explain why it didn’t.
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