Merck & Co MRK.N gained 1% after reporting higher-than-expected second-quarter earnings and revenue. By Shreyashi Sanyal and Aniruddha Ghosh July 28 (Reuters) - Wall Street's main indexes were set to open lower on Thursday following gloomy forecasts from Meta and Qualcomm, while an early reading which showed the U.S. economy contracted again in the second quarter also weighed on sentiment. Fears of runaway inflation and aggressive monetary policy tightening biting into economic growth have spooked markets, after gross domestic product fell at a 0.9% annualized rate last quarter, the Commerce Department said in its advance GDP estimate.