Here are the most important news, trends and analysis that investors need to start their trading day:

• Stock futures turn lower after Fed chief Powell's comments
• AstraZeneca revises Covid vaccine data with lower efficacy rate
• Biden to hold first news conference of his presidency
• Oil prices slide as Covid concerns outweigh Suez Canal disruptions
• Lawmakers to press tech CEOs over speech, misinformation

1. Stock futures turn lower after Fed chief Powell's comments

U.S. stock futures turned lower Thursday after Federal Reserve Chairman Jerome Powell told NPR's "Morning Edition" that Covid economic stimulus and vaccinations allowed the U.S. economy to recover faster than expected and that central bankers, at some point, may be able to pull back emergency support.

Late-day selling reversed gains and dragged the S&P 500 down 0.6% on Wednesday. The Dow Jones Industrial Average dipped lower in the final seconds of Wednesday's session. The Nasdaq dropped 2% after a slightly higher open gave way to a day of selling. Tech stocks were lower despite the 10-year Treasury yield holding below recent a 14-month high as a market rotation out of high-flying growth names continued. The Nasdaq last closed at a record in February. The Dow and S&P 500 last closed at record highs last week.

The Labor Department Thursday morning reported 684,000 new filings for unemployment benefits last week. That was much better than estimates for 735,000, and the first time initial weekly jobless claims was below 700,000 since the Covid pandemic began just over a year ago.

A separate government release Thursday morning showed that U.S. economic growth was stronger than anticipated in the fourth quarter. The third and final reading on Q4 gross domestic product showed a gain of 4.3%, up from previous estimates and the Wall Street consensus of 4.1%.

2. AstraZeneca revises Covid vaccine data with lower efficacy rate

AstraZeneca has issued updated Covid vaccine numbers from its late-stage trial in the U.S. and Latin America after U.S. health officials earlier this week questioned the accuracy of preliminary data. The U.K.-based drug giant now says its vaccine is 76% effective in protecting against symptomatic cases of virus. A release issued on Monday reported an efficacy rate of 79%. AstraZeneca reiterated its two-shot regimen was "well tolerated" among participants and no safety concerns were identified.

3. Biden to hold first news conference of his presidency

The White House announced Thursday that it's dedicating another $10 billion to try to drive up vaccination rates in low-income, minority and rural communities. More than 25% of the entire U.S. population received at least one vaccine dose, including 14% who have been fully vaccinated. The vaccines from Pfizer and Moderna require two shots, while Johnson & Johnson's vaccine is only one shot.

Against the backdrop of rising Covid cases in many states and more than 30 million total U.S. infections, President Joe Biden is set to hold his first presidential news conference. He's expected to point to a surge in vaccinations, encouraging signs in the economy and the benefits Americans will receive from the latest sweeping stimulus package. He's also likely to face a wide range of questions from U.S.-Mexico border security to gun control in the wake of mass shootings in Colorado and Georgia.

4. Oil prices slide as Covid concerns outweigh Suez Canal disruptions

Oil prices fell Thursday as fuel demand concerns reemerged alongside worries about steps back in the global fight against Covid. Prices of U.S. benchmark West Texas Intermediate crude and the Brent international benchmark each dropped roughly 2%, one day after they surged nearly 6% on the shipping disruptions caused by the grounding of a giant container ship in the Suez Canal, a major oil trade route. It could take weeks to clear, according to the CEO of a Dutch company helping with the salvage efforts.

5. Lawmakers to press tech CEOs over speech, misinformation

Big Tech leaders Thursday are scheduled to testify at a virtual House panel hearing on efforts to prevent their platforms from spreading falsehoods and inciting violence. Facebook CEO Mark Zuckerberg, Twitter CEO Jack Dorsey and Alphabet CEO Sundar Pichai, whose company owns Google and YouTube, will face increased pressure following the Jan. 6 insurrection at the U.S. Capitol and the rise in Covid vaccine misinformation. There's increasing support in Congress for imposing new curbs on legal protections regarding speech posted online.

— The Associated Press and Reuters contributed to this report. Get the latest on the pandemic with CNBC's coronavirus blog.