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Currently, there is no approved vaccine for the prevention of infection by West Nile virus. A clinical trial of a possible vaccine is being planned to include subjects treated with the vaccine while other subjects are given a placebo.
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The experiment involves testing a possible vaccine for the West Nile virus. Some subjects will be treated with the vaccine, while others will be given a placebo. Show more…
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To date there is no vaccine available for WNV, although there are some studies underway to develop one. Let us suppose a study of a potential vaccine was done on 150 individuals – all of whom test negative for any past exposure to WNV. A double blind randomized clinical trial is used to compare the vaccine to a placebo, with equal numbers in both groups. All individuals reside in the same area and WNV is endemic to this area. 30 of those who received the placebo contract WNV (indicated by regular blood tests), but among those who receive the vaccine only 3 do at the end of 1 year of follow-up. What is the vaccine efficacy?
A vaccine is a substance that contains all or part of a noninfectious version of a disease-causing organism. When the vaccine is administered to a person, the person's immune system attacks the noninfectious version of the organism and learns to recognize its surface proteins. The next time the immune system comes in contact with the same surface proteins, it has a defense already prepared in order to respond quickly to the invading organism. In this way, a vaccine gives people immunity to the disease-causing organism. Vaccines can be life-saving, but there have been a few cases of people catching a disease from the administered vaccine. How might genetically engineered organisms solve this problem?
In order for a vaccine to be effective, it should reduce a person's chance of acquiring a disease. Consider a hypothetical vaccine for malaria-a tropical disease that kills between 1.5 and 2.7 million people every year. $^{20}$ Suppose the vaccine is tested with 500 volunteers in a village who are malaria free at the beginning of the trial. Two hundred of the volunteers will get the experimental vaccine and the rest will not be vaccinated. Suppose that the chance of contracting malaria is $10 \%$ for those who are not vaccinated. Construct a two-way table to show the results of the experiment if: (a) The vaccine has no effect. (b) The vaccine cuts the risk of contracting malaria in half.
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