The coronavirus pandemic is slowing down businesses and forcing companies to reassess their positions across many sectors, including advertising.

The world's largest agency holding groups, including WPP PLC, Omnicom Group Inc. and Interpublic Group of Cos. Inc., have warned of significant uncertainty about the future. Meanwhile, Wall Street suggests an ad-sector recession is at hand.

WPP, in a March 31 financial update, noted that while media spending at that point had largely remained committed, the company was seeing an increasing number of cancellations and other signs of volatility from clients. As such, it withdrew its financial guidance for the year.

Interpublic's ad research arm Magna Global now expects a 2.8% decline in U.S. ad sales this year, versus its prior projection of 6.6% growth. As the economy stabilizes, Magna sees a second-half rebound and 2.5% growth next year, up from its prior projection of 1.4%. The amelioration reflects delayed consumer consumption, the shift of the Summer Olympics to next year and low comparisons versus 2020. Interpublic withdrew its 2020 financial guidance on March 26.

READ MORE: Sign up for our weekly coronavirus newsletter here, and read our latest coverage on the crisis here.

The consensus view is there will be a deep advertising recession in the second and third quarters of this year, Wells Fargo analyst Steven Cahall wrote in a recent note. The duration of public health restrictions that constrain consumer activity and in turn discourage business investment is the key variable on the contraction, but Cahall foresees the ad market picking up late this year or early in 2021.

In the meantime, there are opportunities for ad clients as viewing has increased significantly across different demographics and dayparts.

The time spent watching television increased 17% in March for viewers over the age of 2, compared with the final week of February, according to a study by VAB, the trade group formerly known as the Video Advertising Bureau. VAB represents many big U.S. TV networks and other premium video providers. Excluding adults, the gains were more dramatic, with viewing up 39% among children ages 2 to 11 and 46% for teens and tweens, largely because of pandemic-driven school closings.

"With so many of us under roofs these days, advertisers would do well to navigate the premium video landscape," said VAB President Sean Cunningham in an interview. Viewers are not only seeking information via newscasts but comfort and entertainment from an array of different content, which opens doors to fresh ways to reach various demos, he said.

Brian Wieser, global president of business intelligence at GroupM, WPP's media investment group, said in some cases companies might be better served to accent their brand values during the health crisis rather than trying to sell products.

Considering the growing unemployment ranks, "you're not going to sell much right now anyway," Wieser said during an April 1 video chat hosted by digital ad targeting platform Simulmedia Inc.

Wieser noted that some apparel brands have been helping to make masks, while hardware companies are manufacturing ventilators or parts for the machines. Other companies, he believes, will reap benefits with consumers from being good corporate citizens in terms of their actions and messaging during this time, once a sense of normalcy returns.

The VAB study indicated 56% of consumers were pleased to hear brands taking actions such as donating goods and services, and 43% said they want to hear reassuring messages from brands they know and trust.

Cunningham said the companies that practice good citizenry via messaging and public demonstrations will be rewarded in terms of their brand equity and profitability.

Unsurprisingly, travel and related industries and movie studios are reducing ad spending as travel and entertainment spending plummets worldwide. Magna pointed to restaurants as a sector facing the biggest ad impact, with retail, finance and automotive also feeling pressure.

Home entertainment and e-commerce have the potential to be two bright spots in the marketplace, according to Magna. GroupM's Wieser said there could be opportunities with home education and home meal preparation.

In a weakened ad environment, Cahall said national TV, with locked-in inventory and a stickier customer base, will fare a bit better than local TV, radio and out-of-home ads. The latter is unlikely to pick up again until social distancing and stay-at-home mandates ease, and that may come in stages, noted Matt Collins, senior vice president of marketing at Simulmedia.