Dengue vaccination trial

A study was conducted to establish whether a new vaccine can prevent the Dengue disease [Kirkpatrick et al, Science Translational Medicine 2016: 8, 330ra36].

In the trial, 21 volunteers were injected with the experimental vaccine, and 20 other volunteers with a dummy vaccine (placebo). Six months later, all 41 subjects were injected with a weakened version of the dengue virus — which usually causes symptoms similar to a mild dengue infection, such as a rash.

None of those vaccinated became sick from the virus or showed the virus in their blood. By contrast, dengue virus was found in the blood of all of the volunteers who had received the dummy vaccine; 80% of them also developed a rash.

The study results can be found in this dataset: DengueVaccine.

  1. Is this study an experiment or an observational study? Why? What are the implications?
  2. Set up hypotheses to test for differences in a) the presence of virus in the subjects’ blood upon virus injection and b) the development of a rash.
  3. While a qualitative assessment of the data appear to show that the vaccine is effective, conduct an appropriate, quantitative statistical analysis to verify such intuition.
  4. Interpret the results of your analysis in the context of the study.