There have been no new cases of naturally occurring polio in North Ame

A[b]
[b]Conclusion: Clearly it is time to switch from OPV to IPV as the most commonly used polio vaccine for North American children.

The conclusion is comapring OPV and IPV.--> One tip is to look for an answer that deals with both OPV and IPV (A, D: D is out of scope, so A is the right answer choice)

You can also spend few more seconds on the answer choices and Nidzo explained every a.c. greatly.

(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.

(B) The vast majority of cases of polio caused by OPV have occurred in children with preexisting but unsuspected immunodeficiency disorders.

(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.

(D) Although IPV is preferred in some European nations, most countries with comprehensive child immunization programs use OPV.

(E) IPV, like most vaccines, carries a slight risk of inducing seizures in children with neurological diseases such as epilepsy.[/b]

Premise - No naturally occurring polio. The cases are due to OPV.
Conclusion - Switch from OPV to IPV would cut the number of cases.

Prethink -
For the problems like this one, in which - we have two causing factors and the argument favors/rejects one for another,
the common approaches to attack are:
1. Show that the two factors are connected or related.
2. Show the benefits of one over threats of another.

e.g. If IPV and OPV are so connected that switch is actually not a considerable approach, then the plan itself falls apart.

(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.
If true, switching from OPV to IPV will not help in reducing the number of cases.
Attacks the argument.
(B) The vast majority of cases of polio caused by OPV have occurred in children with preexisting but unsuspected immunodeficiency disorders.
As soon as I read "polio caused by OPV" , I really don't care about the additional information.
As the choice still believes that "polio caused by OPV" and hence can't attack 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.
Who is talking about lightning?

(D) Although IPV is preferred in some European nations, most countries with comprehensive child immunization programs use OPV.
What most countries do may not be always the efficient thing.
(E) IPV, like most vaccines, carries a slight risk of inducing seizures in children with neurological diseases such as epilepsy.
We must gauge the harms and benefits for the plan.
For a weakening problem -
If a change (for the planned benefit X) brings a "significant" harm Y - the change can't be a good idea.
This choice is not a "good" candidate for weakening the argument only because the choice says " a slight risk".
If I remove the adjective "slight", this could be a potential choice for weakening the argument for the threat it talks about.

A wins over E

IMO A.

due to vaccines **naturally** occurring polio = 0
vaccine 2 types:
1. OPV - # of vaccine caused polio is x.
2. IPV - # of vaccine caused polio is x/2.
OPV is currently used, & causes 12 cases/year of vaccine caused polio. If IPV used it will become 6 cases/year.
=> IPV should be used.

We need to prove that IPV should not be used, with a reason.

(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 option opens up a can of worm, that old problem (naturally occuring polio) going to occur if IPV used. This is definitely weakening the argument. Keep

(B) The vast majority of cases of polio caused by OPV have occurred in children with preexisting but unsuspected immunodeficiency disorders.
This does not weaken by proving why IPV should not be used. Eliminate

(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 gives statistical information on OPV. What about IPV? How can I prove IPV should not be used? This option is useless. Eliminate

(D) Although IPV is preferred in some European nations, most countries with comprehensive child immunization programs use OPV.
This option, with "Preference", does not provide any reasoning why IPV should not be used. Eliminate

(E) IPV, like most vaccines, carries a slight risk of inducing seizures in children with neurological diseases such as epilepsy.
This option misses comparing the risk of IPV with that of OPV. So we don't know which is better, and we are looking for option to say IPV should not be used. Eliminate.

Hence, A is the best answer choice.

Okay I get that but isn't it a premise that new information is entertained in the option choices with a weakening type question?

(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.
OPV compled eradicaed natural infections and only created some fewer non-anticipated cases if IPV is not able tocurtail the former it significantly weakens the argument therefore let us hang on to it

(B) The vast majority of cases of polio caused by OPV have occurred in children with preexisting but unsuspected immunodeficiency disorders.
This lends strength to the fact Opv wasn't the prime cause however this doesn't eleminate the fact that IPV has a better results which we cannot definitively decide therefore out

(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.
IPV rating might better off or worse we cannot quantitatively define therefore out

(D) Although IPV is preferred in some European nations, most countries with comprehensive child immunization programs use OPV.
What others prefer is absolutely inconsequential therefore out

(E) IPV, like most vaccines, carries a slight risk of inducing seizures in children with neurological diseases such as epilepsy.
we don't have the data suggesting the rate OPV therefore out

THerefore IMO A

­Is it not outside information that IPV may cause naturally induced polio??

­Here is my workout -

Recent Yrs : No new (Nat) polio cases in NA.
12 New cases/Yr in NA (OPV) = COUNTER :  IPV ---> OPV/2

SWITCH : OPV--->IPV.

The issue is about Naturally occurring Polio Vs manmade Polio...

Switching from OPV to IPV will result in half but option (A) is the only option which states that it will result in new Naturally occurring cases (Which presently is nil in recent years), which is not acceptable and it goes against the conclusion " Clearly it is time to switch from OPV to IPV as the most commonly used polio vaccine for North American children."

Check all the other options, none touches this point.

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