US pharmaceutical company Pfizer says that a preliminary analysis shows that its COVID-19 vaccine is 90 percent effective at preventing the coronavirus, far exceeding the expectations of the US Food and Drug Administration. While it usually takes many years to develop and widely distribute vaccines, scientists have been trying to get one ready within an unprecedented timeframe as COVID-19 has wreaked havoc around the world. Of the hundreds of candidates in development, only 12 have progressed to Phase III of the clinical trial process, when they are being tested on thousands of people and the results are compared with those who receive a placebo drug. Phase III is the final stage before approval. Who's gotten there so far?