Wall Street struggles for a modest bounce-back

U.S. stocks took a swing at a tentative rebound in the early minutes of Wednesday's session as long-dated debt yields slid back from multi-year highs.

An initial rally turned mixed in the first half hour of trading, with tech pulling the Nasdaq into the red. The small-cap Russell 2000 .RUT is up more sharply than its larger-cap peers, rising 0.9%.

U.S. 30-year Treasury yields pulled back sharply from their highest level in 19 years after the U.S. Treasury announced it would double the size of liquidity support buybacks for long-dated bonds.

Fears of rising interest rates amid mounting sovereign debt and geopolitical uncertainty, which fueled Tuesday's selloff, appear to be easing.

Healthcare stocks .SPXHC led the gainers among the 11 major S&P 500 .SPX sectors, powered by a 120% surge in Moderna shares after its Merck-partnered MRK.N melanoma vaccine reduced the risk of recurrence in a large trial.

Among other winners, gold/silver stocks .XAU, homebuilders .SPCOMHOME and housing .HGX are well ahead of the pack, while aerospace/defense .SPCOMAED and chipmakers .SOX are laggards.

Two big-box retailers reported quarterly results before the bell.

Target TGT.N is up 4.9% after raising its annual sales forecast as its turnaround efforts bore fruit, while Lowe's LOW.N is managing to advance 3.6% even after saying it expects zero same-store sales growth due to consumer caution.

The S&P Retail index .SPXRT is up 0.8%.

Walmart WMT.O is expected to report tomorrow.

Here's where things stood as of 9:54 a.m. ET:

(Stephen Culp)