PrepTest 107, Section 1, Question 10
The symptoms of hepatitis A appear no earlier(59 more words not shown)
Which one of the following,(12 more words not shown)
- AThe placebo did(14 more words not shown)
- BMore members of(26 more words not shown)
- CThe people who(17 more words not shown)
- DThe vaccinated people(16 more words not shown)
- EOf the people(21 more words not shown)
Reading the argument
People in both groups developed symptoms. Then how can the vaccine be completely effective?
One possibility is that the symptoms don't uniquely identify hepatitis A. Imagine a symptom as ordinary as coughing: someone could have it for more than one reason. That is a hypothetical example, not a claim about the symptoms of this disease. It shows why having symptoms associated with an illness needn't, by itself, prove that the person caught that illness after vaccination.
We also have a timing fact to keep straight. Symptoms appear no earlier than 60 days after infection. Seeing symptoms today doesn't tell us that the infection began today. The claim about the vaccine is specifically that it prevents infection, not that it prevents every later appearance of a symptom.
What we’re looking for
To resolve the discrepancy, we need both facts to fit: the vaccine prevents infection, yet some vaccinated people later show symptoms. My first prediction is that something else could account for those symptoms. Let's see whether a choice supplies that explanation or another way for the two facts to coexist.
Working the answers
- A
This concerns side effects from the placebo. It doesn't explain why people who received the vaccine developed symptoms despite the vaccine's effectiveness. Removing a possible explanation for the placebo group's symptoms leaves the puzzling vaccine group untouched.
- B
Recognizing a symptom and having a symptom are different things. Some participants might be better at identifying what they experienced, but the passage already says people in both groups exhibited symptoms. Their ability to name those symptoms doesn't explain why vaccinated people had them.
- C
Better overall physical condition in the placebo group doesn't resolve the apparent conflict. We still need to explain how a vaccine that prevents infection can be followed by symptoms in its recipients. A general comparison of the groups' health supplies no timing or other explanation of those cases.
- DCorrect
The infection happened before the vaccination. That's a different route from our initial thought that the symptoms might have another cause. It uses the delay mentioned in the first sentence.
Picture someone already infected but still within the symptom-free interval receiving the vaccine. Symptoms can appear later because of that existing infection. The vaccine can prevent a new infection without curing an infection that is already present. The later symptoms therefore don't contradict the claim that it completely prevents infection as used in the test.
- E
Faster recovery would be a benefit, but it wouldn't establish prevention. A treatment could help infected people recover while failing to stop anyone from becoming infected. We need to reconcile the symptoms with complete prevention, not merely find some way the vaccine could be useful.
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