By Anna Isaac

U.S. stock futures wobbled Friday, putting the S&P 500 on course for a fourth straight week of losses.

Futures tied to the S&P 500 slipped 0.4%, indicating stocks could lose ground after the opening bell. The index is down more than 2.2% so far this week. Contracts tied to the tech-heavy Nasdaq wavered between small gains and losses.

Investors' confidence has been crimped by elevated levels of new coronavirus infections in the U.S. and Europe, as well as some signs that the global economic recovery is slow and uneven. The uncertainty and political risks generated by November's presidential election is also adding to the jitteriness in markets.

"We're in a bit of a holding pattern. It feels like a bit of a phony market right now. I don't think there's any key factors that have changed," said David Coombs, head of multiasset investments at Rathbone Brothers. "Until we get a vaccine for the population at large, the coronavirus course is uncertain."

Investors are also awaiting signs of progress on additional U.S. stimulus spending from the government. House Democrats are readying a scaled-down package of around $2.4 trillion that would include assistance to airlines, restaurants and small businesses, according to people familiar with the matter. But Republicans said the chances of a deal before Election Day remained slim.

"We've had such a huge fiscal response already, it's easy to say the response now is disappointing," said Holger Schmieding, chief economist at Berenberg Bank. "It's basically a matter of time: before or after the election. Significant support is coming. The Fed is asking for it."

The U.S. reported about 44,000 new coronavirus cases Thursday, up from about 37,000 a day earlier and bringing the total number of people who have been infected in the country to about 6.98 million, according to data compiled by Johns Hopkins University. Daily new infections have been going up again since mid-September.

New data on durable goods orders, due out at 8.30 a.m. ET, will offer investors a view on whether U.S. manufacturers have continued to stage a rebound from shutdowns and supply-chain disruptions related to the pandemic. Orders in August for products designed to last at least three years are likely to post their fourth consecutive monthly gain. But economists are forecasting a slowdown in the pace of improvement in overall demand and underlying business investment amid uncertainty about the path of Covid-19.

Economic data will need to show continuous improvement if gains in stocks are going to be sustained, investors warned.

"As we go into the fourth quarter, risks are starting to pile up, making it harder for equities to make gains. It's the election risk, the Covid risk, and the fiscal risk," said Seema Shah, chief strategist at Principal Global Investors. "And then of course the economic data: we've had all the easy gains in the third quarter and we want to be sure that momentum isn't running out."

In bond markets, the yield on the U.S. 10-year Treasury ticked down to 0.660%, from 0.664% Thursday.

Shares of Novavax rose 6.6% in off-hours trading after the company said Thursday it has started a final-stage study of its experimental Covid-19 vaccine in the U.K. The stock, which has been popular among investors using the Robinhood app, has gained over 2,470% this year.

Overseas, the pan-continental Stoxx Europe 600 fell 0.6%.

In commodities, gold slid 0.7% to $1,863.80 a troy ounce. The precious metal is on course for its worst week in six months, hit on two sides by a strengthening dollar and falling inflation expectations.

The major Asian equity benchmarks ended the week on a mixed note. Japan's Nikkei 225 rose 0.5% Friday, while China's Shanghai Composite Index ticked down 0.1%.

Write to Anna Isaac at anna.isaac@wsj.com