U.S. high-yield bond funds saw their biggest outflows in eight months in November, largely owing to the prospect of the Federal Reserve raising interest rates sooner than expected and, to some extent, the concerns over the Omicron coronavirus variant.

According to Refinitiv Lipper data, U.S. high-yield bond funds faced an outflow of $4.2 billion in November - the biggest since March.

The ICE BofA U.S. High Yield Index, a commonly used benchmark for the junk bond market, dropped 1% last month, the biggest fall since September 2020.

The index's option-adjusted spread, which measures how much premium riskier companies should pay compared with what the government pays, widened to 367 basis points at the end of last month, from 308 basis points a month earlier.

Ryan O'Malley, fixed income portfolio strategist at Sage Advisory Services, said the main reasons for outflows from high-yield bonds were concerns over the hit to the "reopening trade" from the Omicron variant, particularly for the energy and transport sectors.

"The prospect of accelerated tapering of quantitative easing" has also affected flows, he said.

The iShares iBoxx $ High Yield Corporate Bond ETF HYG led with outflows worth $1.35 billion, while BlackRock High Yield Bond Portfolio; Institutional and Fidelity Capital & Income fund faced net sales of $850 million and $406 million, respectively.

Some analysts also said investors were cutting their positions in high-yield debt as they were not keen to carry risks into the year-end.

U.S. companies have also borrowed a record $406 billion worth of high-yield debt so far this year, which has increased the supply of junk bonds in the market.

"There is some concern that new issue supply overshot demand, particularly in the face of a less accommodative Fed," said O'Malley.

The uncertainty around the Fed's future rate path and low liquidity have also increased volatility in the bond markets, prompting higher outflows from high-yield bonds, analysts said.

The ICE BofA MOVE index, which measures one-month expected swings in U.S. bonds, is trading at its highest level since March 2020.

"But it’s important to keep in mind that while high yield is the riskiest of the fixed-income asset classes, it’s also the least risky of the risk asset classes," said Colin Robertson, head of fixed income at Northern Trust Asset Management.

(With additional Reporting by Gaurav Dogra in Bengaluru Editing by Vidya Ranganathan and Aditya Soni) ((patturaja.murugaboopathy@thomsonreuters.com;))