Wall Street stocks were mixed early Friday following a promising announcement from Merck on a therapeutic for Covid-19 as US data showed another rise in inflation.

Analysts cheered news from Merck and partner Ridgeback Biotherapeutics that a clinical trial of their oral antiviral prospect showed about a 50 percent reduction in the risk of hospitalization or death from Covid-19.

LBBW Bank's Karl Haeling said the Merck announcement had the potential to be a "game changer" in the pandemic.

But the good news from Merck was offset by inflation data.

The Commerce Department's personal consumption expenditures price index was up 4.3 percent from August 2020 as the world's largest economy struggles with supply chain delays and shortages amid its bounceback from the pandemic's business closures.

About 20 minutes into trading, the Dow Jones Industrial Average was up 0.3 percent at 33,942.32, with Merck surging more than eight percent.

The broad-based S&P 500 was up a hair at 4,308.86, while the tech-rich Nasdaq Composite Index shed 0.2 percent to 14,421.14.

Markets are also monitoring developments on Capitol Hill. On Thursday, lawmakers agreed to a stopgap spending bill that avoided a government shutdown.

But difficult negotiations remain unresolved on raising the debt ceiling and enacting President Biden's infrastructure and social spending agenda.

Coronavirus