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.

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.

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.

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.

This does not affect the argument. Both OPV and IPV are vaccines—this would apply to both equally.