Many vaccines lose their effectiveness if they are allowed to warm, and some are damaged by freezing as well, which leaves a narrow band of temperature that must be maintained from the factory to the arm. The chain of refrigeration that does this is the expensive and fragile part of any immunisation campaign, far more so than the vaccine itself. A single failure at one point in the chain can spoil an entire consignment without any visible sign that anything is wrong. Programmes therefore carry temperature indicators alongside the doses, because a vial that has been spoiled looks exactly like one that has not.
According to the passage, temperature indicators are carried because
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Correct answer to question 51 (Paragraph Comprehension): a spoiled dose looks the same as a good one
Method
The final clause gives the reason directly. The second choice reverses the passage, which says the refrigeration chain costs far more than the vaccine.
Updated: November 2026
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