LSAT 120 – Section 1 – Question 19

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PT120 S1 Q19
+LR
Weaken +Weak
Causal Reasoning +CausR
Net Effect +NetEff
Value Judgment +ValJudg
A
63%
165
B
25%
159
C
2%
155
D
1%
157
E
10%
160
146
157
168
+Harder 145.819 +SubsectionMedium

There have been no new cases of naturally occurring polio in North America in recent years. Yet there are approximately 12 new cases of polio each year in North America, all caused by the commonly administered live oral polio vaccine (OPV). Substituting inactivated polio vaccine (IPV) for most childhood polio immunizations would cut the number of cases of vaccination-caused polio about in half. Clearly it is time to switch from OPV to IPV as the most commonly used polio vaccine for North American children.

Summarize Argument
IPV should be the most commonly used polio vaccine for North American children, instead of OPV. OPV causes all new cases of polio each year in North America, and IPV would reduce the number of cases by half.

Notable Assumptions
The author assumes that IPV does not have serious side effects that make it undesirable for use on most children—side effects that may outweigh the benefit of decreasing the number of cases of live polio a year. Furthermore, the author assumes that there are no other significant undesirable consequences that could arise from the proposed switch.

A
If IPV replaces OPV as the most commonly used polio vaccine, at least a few new cases of naturally occurring polio in North America will result each year.
This weakens the argument. It exploits the author’s assumption that there are no significant undesirable consequences that could arise from the switch. (A) says if IPV replaces OPV, naturally occurring polio would result—something which has not occurred in recent years.
B
The vast majority of cases of polio caused by OPV have occurred in children with preexisting but unsuspected immunodeficiency disorders.
This does not affect the argument. The author advocates for a switch to IPV to reduce the annual number of polio cases. The specific characteristics of these cases—such as whether the affected children had undiagnosed immunodeficiency disorders—do not weaken the argument.
C
A child’s risk of contracting polio from OPV has been estimated at 1 in 8.7 million, which is significantly less than the risk of being struck by lightning.
This does not affect the argument. The author does not dispute the idea that the risk is slight; rather, the author argues that the risk could be further reduced by switching to IPV.
D
Although IPV is preferred in some European nations, most countries with comprehensive child immunization programs use OPV.
This does not affect the argument. The author’s argument is supported solely by evidence from North America, and the conclusion is specific to North America as well. What other continents or countries are doing is not relevant.
E
IPV, like most vaccines, carries a slight risk of inducing seizures in children with neurological diseases such as epilepsy.
This does not affect the argument. Both OPV and IPV are vaccines—this would apply to both equally.

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