Question

Some batches of polio vaccine used around 1960 were contaminated with SV40, a virus that in monkeys causes various cancers. Some researchers now claim that this contamination caused some cases of a certain cancer in humans, mesothelioma. This claim is not undercut by the fact that a very careful survey made in the 1960s of people who had received the contaminated vaccine found no elevated incidence of any cancer, since ................

• A. Most cases of mesothelioma are caused by exposure to asbestos
• B. In some countries, there was no contamination of the vaccine
• C. SV40 is widely used in laboratories to produce cancers in animals
• D. Mesotheliomas take several decades to develop
• E. Mesothelioma was somewhat less common in 1960 than it is now

Hint:

When evaluating long-term health studies, consider the latency period of diseases that take years or decades to develop.

Answer 1

The Correct Option is D

Step 1: Understanding the argument.
The argument presents a claim about polio vaccines causing cancer, but the claim is challenged by the survey showing no elevated cancer rates. The key issue is the long latency period for mesothelioma.
Step 2: Analyzing the options.
- (A) This is relevant to mesothelioma but does not address the long latency period of the cancer.
- (B) The fact that some countries didn’t have contaminated vaccines doesn’t impact the claim that the contaminated vaccines could have caused cancer.
- (C) This does not address the issue of the long latency of mesothelioma and does not support the claim.
- (D) This is the correct answer. Mesotheliomas have a long development period, so the survey conducted in the 1960s may not have detected the cancers that would develop many years later.
- (E) This doesn’t address the key issue of cancer development latency.
Step 3: Conclusion.
The correct answer is (D), as it explains why the survey from the 1960s may not have detected cases of mesothelioma caused by the contaminated vaccine.