The CDC is tracking 200 experimental vaccines aimed at ending the pandemic, a scientific quest moving forward at record-breaking speed.Vaccine development usually takes years and unfolds step by step. Experimental vaccine candidates are created in the laboratory and tested in animals before moving into progressively larger human clinical trials.These steps are now overlapping in the race to find a vaccine. Human testing began in some cases before animal studies were finished.The Food and Drug Administration says a vaccine for Covid-19 will need to prevent disease or decrease symptoms in at least 50 percent of those who receive it. According to the Centers for Disease Control and Prevention, the effectiveness of the flu vaccine ranges from 40 to 60 percent.The U.S. government has invested about $9.5 billion to speed up development and jump-start manufacturing. Vaccines work by teaching the body’s immune system to recognize and block viruses. Each category of vaccine technology works under this basic principle.Some vaccines do not specifically target the coronavirus but aim to increase the body’s first line of immune defenses.Read more at the Wall Street Journal: https://wapo.st/3lhKK0u