(Bloomberg) -- The takeover game is rampant among U.S. health insurers and stock investors are filling the stands.

The iShares U.S. Healthcare Providers exchange traded fund has attracted $247 million in net inflows this year, the biggest first-half total since it started trading in May 2006. The ETF has gained 21 % in 2015, seven times more than the Standard & Poor’s 500 Index and almost twice a benchmark gauge of health-care stocks.

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