PrepTest 120, Section 1, Question 19
There have been no new cases of naturally(76 more words not shown)
Which one of the following,(6 more words not shown)
- AIf IPV replaces(25 more words not shown)
- BThe vast majority(17 more words not shown)
- CA child's risk(25 more words not shown)
- DAlthough IPV is(14 more words not shown)
- EIPV, like most(16 more words not shown)
Reading the argument
Reducing vaccine-caused polio from about twelve cases to about six sounds good. But what happens to naturally occurring polio?
The passage says there haven't been new natural cases in recent years. That doesn't mean we can forget about preventing them. Perhaps the current vaccination approach helps keep those cases from occurring. If the replacement vaccine doesn't protect as well, reducing one source of cases could bring another source back.
That's the comparison I'd want before recommending the switch. Suppose we prevent six vaccine-caused cases but the change allows hundreds of natural cases. The improvement on one measure wouldn't make the overall change worthwhile. Those numbers are an illustration of the concern, not a prediction about either vaccine.
What we’re looking for
For a weakener, I'd look for evidence that switching to IPV sacrifices some protection against natural polio. We don't have to prove the switch would be disastrous. A fact that gives us reason to question the claimed benefit can be enough.
Working the answers
- ACorrect
The switch would bring at least a few naturally occurring cases each year. That gives us the drawback we were looking for: the reduction in vaccine-caused cases would come with some new natural cases.
“A few” is weaker than my imagined hundreds. If the switch prevented six cases and brought two new ones, the total would still fall from twelve to eight. So A doesn't prove switching is a bad idea. It does show that counting only the six prevented cases overstates the benefit, making the recommendation less convincing. A weakener needn't completely reverse the decision.
- B
This identifies which children suffered most of the vaccine-caused cases. It doesn't tell us whether IPV would protect those children better or whether the switch would create another problem. The fact that the disorders were unsuspected also doesn't itself give us an available way to avoid these cases while keeping OPV.
- C
A very small risk is still a risk that another approach might reduce. Comparing it with lightning doesn't compare OPV with IPV. If the alternative reduced that risk without an offsetting drawback, the argument for switching could still make sense.
- D
Other countries' choices don't tell us what switching would accomplish for North American children. We'd want to know why those countries use a particular vaccine and whether the relevant conditions match, rather than treat a count of countries as the needed comparison.
- E
A seizure risk is a real concern, so this deserves a careful look. But does switching increase that risk? E says IPV shares it with most vaccines and gives no comparison with OPV. OPV might carry the same risk. We shouldn't assume it definitely does, but we also can't assume IPV introduces a new disadvantage. A expressly identifies a consequence of replacing OPV; E identifies a possible cost of IPV without establishing that the switch adds it.
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