The Federal Reserve made few splashes on its first day of buying corporate bond ETFs, which had already seen dramatic improvements in recent weeks after the March sell-off.

In an unprecedented move, the U.S. central bank said it would begin buying corporate bond exchange-traded funds May 12 that primarily give broad exposure to investment-grade bonds in addition to some that track high-yield ones. The largest vehicles falling under those criteria seemed to have shrugged off the news, though.

BlackRock Inc.'s iShares iBoxx $ Investment Grade Corporate Bond ETF, known by its ticker of LQD, closed trading 0.96% higher on the day. Vanguard Group Inc.'s Intermediate-Term Corporate Bond ETF, VCIT, ticked up 0.48%. Two high-yield ETFs that analysts say may also be part of the Fed's purchasing plans, HYG and JNK, ended trading down slightly but were still higher than the broader market. The iShares iBoxx $ High Yield Corporate Bond ETF, HYG, fell 0.13%. State Street Global Advisors Inc.'s JNK, the SPDR Bloomberg Barclays High Yield Bond ETF, dropped 0.05%.

"Ultimately, in my mind, the significance of this more so than anything is going to be the lasting effect," said Ben Johnson, Morningstar Inc.'s global head of ETF research, in an interview. "For all intents and purposes, the Fed has given the ETF wrapper its seal of approval."

The Fed has not yet disclosed the specific bond ETFs it is purchasing, although its announcement in late March that it would wade into corporate bond markets quickly led to a turnaround in the sector after its prior turmoil.

Investors have shifted back into corporate bond ETFs that may be eligible for Fed purchases after the sector saw major outflows in March. According to data from the Investment Company Institute, bond ETFs saw five straight weeks of net inflows after posting net outflows exceeding $21 billion and $10 billion in the weeks of March 18 and March 25, respectively.

The ETF-buying effort is the Fed's first direct foray into the corporate bond market as the coronavirus continues to rattle the U.S. economy. Next up for the Fed is buying up individual corporate bonds under the Secondary Market Corporate Credit Facility and a Primary Market Corporate Credit Facility, which the New York Fed said May 11 will occur "in the near future."

In all, the two facilities will make up to $750 billion in purchases, with the Treasury Department kicking in $75 billion to provide a credit backstop under the program. The Treasury Department said in a news release that it already transferred $37.5 billion toward the SMCCF and PMCCF.

"Together, they will provide up to $750 billion in liquidity and help ensure large employers have access to the credit they need to maintain their business operations and payroll through this challenging period," Treasury Secretary Steven Mnuchin said in a news release.

BlackRock, the world's largest asset manager, is acting as the initial investment manager of the corporate bond facilities for the New York Fed. It has said it will not charge any asset management fees for funds held under the SMCCF.

The Fed may opt against buying some potentially eligible bond ETFs as part of its program, said Todd Rosenbluth, head of ETF and mutual fund research at CFRA. But its willingness to buy underlying corporate bonds in the coming weeks has benefited bond ETFs across the board, he added.

"If the Fed didn't buy your bond ETF, that doesn't matter," Rosenbluth said in an interview. "They’re helping to support the underlying bond market, and that's a positive."