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October 2005 LSAT Section 1 Question 19

There have been no new cases of naturally occurring polio in North America in recent years. Yet there are approximate...

DavidW on May 5, 2020

Answer Choice A

Hi! Could you please explain why answer choice A is the correct answer choice? Thank you!

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SamA on May 8, 2020

Hello @DavidW,

Let's break down this argument. There are currently no new cases of naturally occurring polio. The OPV causes 12 cases per year. The IPV would cause half of that number. Therefore, we should switch to the IPV.

To weaken this argument, we are looking for something that suggests we should not switch to the IPV. This may be a disadvantage to the IPV that wasn't in the stimulus, or it may be an advantage of the OPV that wasn't included either.

Answer choice A is the former. It tells us that the IPV will allow some naturally occurring cases, which the OPV would have prevented. If we were to switch, it is possible that the total polio cases (natural and vaccine-caused), could increase or stay the same. This is a reason not to choose the IPV.