PrepTest 123, Section 2, Question 15
A new government policy has been developed to(84 more words not shown)
Which one of the following(13 more words not shown)
- AThe number of(15 more words not shown)
- BThe likelihood that(11 more words not shown)
- CNo vaccine for(12 more words not shown)
- DEach year the(24 more words not shown)
- EEach year's vaccine(21 more words not shown)
Reading the argument
Why would we need a vaccine for a different strain every year? Giving people an annual vaccination is one thing. Changing which strain it protects against every year is another.
Suppose the strain expected to be most common is X this year. Next year it's Y. So far, different strains. But what if the following year's forecast is X again? Or what if X is the expected strain two years in a row? The policy could keep operating exactly as described without always choosing a strain it hasn't chosen before.
I also want to check whether one vaccination could cover several strains. The passage settles that for this policy: each year's vaccination protects only against the strain deemed most likely to be prevalent that year. So I can't use multiple-strain protection as an objection. The open question is whether the selected strain can repeat.
What we’re looking for
Now we're asked for an assumption that makes the conclusion follow. We need to close that opening. If the strain selected each year has never been selected before, the one-strain vaccination described in the policy will have to target a different strain each year. That's the connection I want.
Working the answers
- A
Keeping the high-risk group the same size doesn't keep the virus the same or make it different. The policy could vaccinate exactly the same number of people each year against strain X each time. We need a reason the targeted strain changes, not a fact about how many people need vaccination.
- B
A greater or smaller risk of an epidemic doesn't establish which strain the vaccination will target. Even if the danger varies, the same strain could remain the one expected to be most common. B leaves our objection untouched.
- C
This may feel useful because it rules out a vaccine covering several strains. But the policy already tells us that each year's vaccination protects only against the strain selected for that year. The problem is whether that selected strain changes.
Imagine every vaccine protects against just one strain and X is selected both this year and next year. C is true, yet the policy doesn't require a vaccine for a different strain next year. So C cannot establish the conclusion. It doesn't contradict the passage; it fails to provide the missing connection.
- DCorrect
Each year's selected strain has never been selected before. That rules out both ways our example allowed repetition: X cannot be selected in consecutive years, and it cannot return after a year of Y.
Combine this with the stated limit on the vaccination: it protects only against the strain selected for that year. A newly selected strain therefore requires a vaccination targeting that different strain. Now the conclusion follows from the policy and the assumption.
- E
Fewer side effects might make a vaccine preferable, but that doesn't establish that it protects against a different strain. A safer vaccine could target the very same strain as last year's. We're trying to establish the changing target, not an improvement in side effects.
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