Explain how a neutralization test is used to determine a vaccines efficacy.

From the text:

Neutralization tests "involved mixing blood serum from newly vaccinated children with live poliovirus and cells in culture. If the vaccine worked, the serum from a vaccinated child’s blood would block the poliovirus and protect the cells. If it didn’t work, the virus would infect the cells, causing damage scientists could see using a microscope. The trouble was, at that point, the cells used in neutralization tests came from monkeys, which were killed in the process. This was a problem, not because of concern for animal welfare—which wasn’t the issue then that it is today—but because monkeys were expensive. Doing millions of neutralization tests using monkey cells would cost millions of dollars."