A health-care venture initiated with astonishing fanfare by three of the world’s most prominent companies-Amazon.com Inc, Berkshire Hathaway Inc. and JPMorgan Chase & Co. and their chief executives are folding around three years after their founding.Haven Health, triggered off by an idea from JPMorgan Chief Executive Jamie Dimon and supported by Amazon’s Jeff Bezos and Berkshire’s Warren Buffett, sought to “transform health care” and minimize costs for hundreds of thousands of workers at three companies by assembling resources and technology.The joint venture, which was announced in 2018 with anticipations high enough to push down main insurers’ shares, will end operations in February without having achieved those aims.Haven’s reframing ambitions proved too difficult to achieve, according to people familiar with the matter. Its shutdown involves the challenges of making drastic changes to the US health-care system and of introducing innovations to hundreds of thousands of employees around the country working at various companies, the people said.