By Caitlin Ostroff and Caitlin McCabe

The Dow Jones Industrial Average tumbled Tuesday as concerns about elevated Covid-19 infection levels and a new strain of the virus in Europe overshadowed Congress' approval of a Covid-19 relief package.

The index of blue-chip stocks fell 200.94 points, or 0.7%, to 30015.51, marking its largest one-day point and percentage decline in December. The S&P 500 slid 7.66 points, or 0.2%, to 3687.26 to extend its losing streak to a third session.

The tech-heavy Nasdaq Composite, in contrast, rose 65.40 points, or 0.5%, to 12807.92, a new all-time high.

Much of the stock market has lost steam this week as some nations began taking steps to curtail travel in an effort to contain the emergence of a fast-spreading variant of coronavirus from England. The U.K. imposed stringent restrictions on social and business activity, prompting concern that more countries may be required to adopt measures that would hamper the global economic recovery.

"It would be a brave man to suggest this will just remain a U.K.-specific issue," said Derek Halpenny, head of research for global markets in the European region at MUFG Bank. "Are we going back into another phase of more pronounced global lockdowns again?"

Oil prices slipped for a second day amid growing worries over the new restrictions imposed on travelers from the U.K. to other countries. Brent crude futures, the benchmark in international energy markets, dropped 1.6% to $50.08 a barrel.

Meanwhile, the yield on the 10-year note ticked down to 0.917%, from 0.941% Monday, as some investors looked to the relative safety of U.S. government bonds. Yields fall when prices rise.

Investors are trying to gauge whether the new strain of Covid-19 will impact the efficacy of vaccines that are being rolled out this month.

BioNTech Chief Executive Ugur Sahin said the vaccine developed by his company, in partnership with Pfizer, would likely work against the new variant and is being tested. If a new mutation would make the current vaccine ineffective, BioNTech can develop another tailored to the new variant in six weeks, he said.

"The big unknown is to what degree could the new strain make the efficacy of the vaccine lower," said Peter Garnry, head of equity strategy at Saxo Bank. "If it just turns out to be more infections, and it doesn't have an effect on the vaccine, then the market will be less concerned."

Late Monday, a fresh $900 billion fiscal stimulus package was passed by Congress, ending weeks of anticipation from investors about whether lawmakers could end their stalemate. The bill, which includes direct checks to households and relief for small businesses, is expected to be signed by President Trump.

Even so, the bill's passage wasn't enough to propel the broader stock market higher.

"We've had the positive news on the vaccines and the fiscal deal, so there's probably not a catalyst to drive stocks meaningfully higher in the next few weeks," said Brian Levitt, global market strategist at Invesco.

Still, Mr. Levitt noted that he maintains a positive outlook on equities.

"In my opinion, betting against stocks over the next year and beyond is betting against medicine, science and policy makers," he said. "And I'm not willing to make those bets."

In corporate news, Apple rose $3.65, or 2.9%, to $131.88 after Reuters reported that the iPhone maker intends to move forward with its own self-driving car technology.

Exercise-equipment maker Peloton Interactive gained $16.82, or 12%, to $161.21, hitting a new all-time-high, after it agreed to buy commercial fitness-equipment provider Precor for $420 million in cash.

Travel stocks and shares of energy companies tumbled. Norwegian Cruise Line Holdings slid $1.70, or 6.9%, to $23.08. Chevron fell for an eighth consecutive day, losing $1.73, or 2%, to $84.36. That marks the longest losing streak for the oil giant since October 2013.

Meanwhile, Tesla tumbled $9.52, or 1.5%, to $640.34, extending its losses for the week to nearly 8%. The electric-car maker made its S&P 500 debut Monday.

Moves in stocks could be big and markets may be especially choppy in coming days because fewer people are trading as the holiday period starts, said Salman Ahmed, global head of macro at Fidelity International.

The final stretch of trading in December is historically positive for the stock market. But this week's losses may be a sign that investors are starting to take profits after a blockbuster year, especially as they consider the possibility of tax changes after President-elect Joe Biden takes office, said JJ Kinahan, chief market strategist at TD Ameritrade. The S&P 500 is up 14% in 2020, and the Nasdaq Composite has catapulted 43% higher.

Additionally, Mr. Kinahan noted, Tuesday's worse-than-expected consumer confidence report may also be weighing on markets.

The Conference Board, a private research group, said its index of consumer confidence dropped to 88.6 in the first two weeks of December, from a revised 92.9 in November. Economists surveyed by The Wall Street Journal had expected a level of 97.5.

Still, there were small signs of optimism. Data from the Commerce Department showed Tuesday that U.S. gross domestic product -- the value of all goods and services produced across the economy -- increased at an annualized rate of 33.4% in the third quarter, slightly stronger than the previous estimate issued last month.

Overseas, European shares rebounded after Monday's losses. The pan-continental Stoxx Europe 600 gained 1.2%.

Major stock indexes in Asia closed lower. China's Shanghai Composite fell 1.9%, and South Korea's Kospi declined 1.6%.

Write to Caitlin Ostroff at caitlin.ostroff@wsj.com and Caitlin McCabe at caitlin.mccabe@wsj.com

(END) Dow Jones Newswires

12-22-20 1726ET