Investors in the vaccine maker Novavax (NASDAQ:NVAX) stock witnessed rollercoaster trading in September and October. Source: Ascannio/Shutterstock.com NVAX stock ended August shy of $240. By Sept. 8, the shares approached $280. Yet now, they are hovering just below $150. In other words, the record high of $331.68 seen in early February is now in the…