By Mischa Frankl-Duval and Akane Otani

U.S. stocks slipped Wednesday as mounting coronavirus cases forced more parts of the country to impose restrictions meant to fight the spread of the virus.

Over the past month, investors have had to weigh progress made on coronavirus vaccines against news that much of the country is reporting a record number of new cases on many days. Stocks have rallied for much of this period, though there have been some days of heavy selling.

"It's been kind of nerve-wracking from an investor standpoint," said Lindsey Bell, chief investment strategist at Ally Invest. While Ms. Bell believes that a successful vaccine will allow economic growth to bounce back in the next year, she also anticipates markets will remain volatile for the foreseeable future.

"There's still lots of concerns and questions marks in the near term," she said.

The Dow Jones Industrial Average shed 344.93 points, or 1.2%, to 29438.42, closing near its lows after coming within striking distance of a record earlier in the session. The S&P 500 fell 41.74 points, or 1.2%, to 3567.79 and the Nasdaq Composite lost 97.74 points, or 0.8%, to 11801.60.

Pfizer shares rose 28 cents, or 0.8%, to $36.32 after the drugmaker said it plans to seek authorization for its vaccine within days. Final results from its joint clinical trial with BioNTech showed its coronavirus inoculation was 95% effective.

Meanwhile, shares of health insurers were among the worst performers in the stock market Wednesday, with UnitedHealth falling $7.59, or 2.2%, to $344.51 and Cigna falling $3.88, or 1.8%, to $210.93.

Target's shares added $3.81, or 2.3%, to $166.85 after the retailer said sales rose steadily in its most recent quarter as demand for household goods and home-office supplies continued to grow during the pandemic.

Shares of companies that have benefited from more individuals working from home also rose. Zoom Video Communications climbed $13.41, or 3.3%, to $415.04.

Heading into the final months of the year, investors say a litany of concerns including new restrictions on social and business activity, and the halting pace of economic recovery, are weighing on overall sentiment.

On Wednesday, for instance, New York City said public schools would halt all in-person instruction starting the following day in an effort to stem the spread of the virus. Other parts of the country have restricted hours for businesses and restaurants and issued travel warnings ahead of the holidays.

Given the speed with which the virus is spreading, many investors and analysts say they are banking on hopes that the U.S. will be able to soon distribute an effective vaccine.

"Given the nature of this crisis, the only way to get out of this cycle of first wave, second wave, third wave [of infections] is to start circulating a vaccine, and that's going to begin relatively shortly," said James McCormick, a strategist at NatWest Markets. "If you can convince the consumer to both re-engage in the economy, and also that they'll have a job in the next six months, that unleashes a major sector of the economy."

Federal Reserve Chairman Jerome Powell on Tuesday cautioned that the economy faces significant challenges and uncertainty because of the increased spread of the coronavirus. He also said it was too soon to say how a potential vaccine would change the outlook, with the possibility of widespread vaccination still many months away.

Overseas, the pan-continental Stoxx Europe 600 ticked up 0.4%.

Most major Asian equity benchmarks ended the day higher. Japan's Nikkei 225 index dropped 1.1% by the close of trading after local authorities said there had been a jump in coronavirus cases.

Write to Mischa Frankl-Duval at Mischa.Frankl-Duval@wsj.com and Akane Otani at akane.otani@wsj.com

(END) Dow Jones Newswires

11-18-20 1657ET