Pfizer's experimental vaccine solving their COVID-19 crisis any time soon.The world cheered on Monday when Pfizer Inc announced its shot, jointly developed with BioNTech SE, was more than 90% effective based on initial trial results.Yet health experts cautioned that the vaccine, should it be approved, was no silver bullet - not least because the genetic material it's made from needs to be stored at temperatures of minus 70 degrees Celsius (-94 F) or below.Such requirements pose a particularly daunting challenge for countries in Asia, as well as in places like Africa and Latin America, where intense heat is often compounded by poor infrastructure that will make it difficult to keep the "cold chain" intact during deliveries to rural areas and.