SHANGHAI, Aug 19 (Reuters) - China’s central bank set its official yuan midpoint slightly higher on Thursday, lifting its value against the currencies of its major trading partners to a fresh 5-1/2-year high. The People’s Bank of China (PBOC) set the midpoint at 6.4853 yuan per dollar prior to the market open, 62 pips or 0.1%, stronger than the previous fix of 6.4915. The stronger official guidance rate has pushed China’s trade-weighted yuan basket index to 98.88, the highest since March 10, 2016, and up 4.26% so far this year, according to Reuters’ calculations based on official data. (Reporting by Winni Zhou and Andrew Galbraith Editing by Shri Navaratnam)