U.K. Prime Minister Boris Johnson kicked off 2021 by locking down his country yet again as new mutations of the COVID-19 virus, potentially more deadly than the last, spread across the nation.

Now those mutations have been discovered in the U.S., and because President Biden's advisors previously said new four- to six-week lockdowns could help defeat the old coronavirus outbreak, investors should consider the implications for business if he "follows the science" and goes for yet another lockdown.

The last time, it was supposed to be just two weeks to bend the curve, and it ran into months. There are numerous businesses still not fully reopened almost a year later, so new lockdowns could be devastating. Here are some the industries that are most at risk.

Sorry we're closed sign hung on window

Image source: Getty Images.

Entertainment

The movie theater industry is already on the brink of ruin because it's running at minimal capacity and there are few movies in theaters to go see.

AMC Entertainment Holdings (NYSE:AMC) only just staved off bankruptcy by raising almost $1 billion from its lenders to survive through 2021, but only if the economy reopens, movie studios release films into theaters again, and Hollywood starts making new movies. If the spigot is turned off more, it and other cinema operators could collapse.

Studios are using their streaming services to funnel movies to consumers, sometimes undercutting the theaters' window of exclusivity. AT&T's (NYSE:T) Warner Bros. studio is releasing all of its 2021 slate of movies to HBO Max on the same day they hit theaters, while Disney (NYSE:DIS) says 80% of the 100 or so movies and TV shows it has planned for the future will go to its Disney+ service or other direct-to-consumer services.

Disney needs to bolster its streaming service because its theme parks are operating at less than optimal capacity, and Disneyland in California remains closed, even as the state's governor declared Hollywood studios essential businesses in his new lockdown orders.

Similarly, Comcast's (NASDAQ:CMCSA) Universal Studios theme park in California is closed, though its parks have reopened elsewhere, but new lockdowns would further widen the losses this segment is wreaking on their financial statements.

Restaurants

The restaurant industry barely survived the pandemic, subsisting on takeout and delivery until indoor seating was allowed once again. Yet with severely reduced seating capacity, chains resorted to outdoor seating in their parking lots to help make up the difference. 

Certain casual dining operators like Darden Restaurants (NYSE:DRI) did better than most because they had previously established a robust off-premise business before the pandemic hit, while fast-food chains like McDonald's (NYSE:MCD) with their drive-thru windows and third-party delivery services, also came through -- if not unscathed, certainly in a better position than family and fine-dining chains.

The drive-thru has also become crucial to fast-casual leader Chipotle Mexican Grill (NYSE:CMG) and even Shake Shack (NYSE:SHAK), which has committed to punching holes in the walls of its restaurants wherever it can to install drive-thru and walk-up windows.

Eatertainment giant Dave & Buster's (NASDAQ:PLAY), though, did not fare well because it had no takeout business to fall back on. Its entertainment-oriented atmosphere of arcades and gaming is only conducive to an in-restaurant experience.

While the industry has learned valuable lessons about how to operate in the future, new lockdowns could still devastate restaurants since reduced volumes will eventually eviscerate their financial statements. 

Travel and tourism

As noted above, theme parks would undoubtedly feel the swift impact of a shutdown, but the industries that even tangentially support the parks would be put at risk of going under.

Airlines, for example, fly families to these vacation destinations, and would be at risk of going under -- though plummeting demand for business travel is what would likely seal their fate. Carrying large amounts of debt and struggling through an extended period of reduced demand, not even converting their planes over from passenger to cargo as some are doing would offset the loss of business.

American Airlines Group (NASDAQ:AAL), which started carrying cargo for the first time in 36 years last year, is burning through cash at a rate of $30 million a day, or some $11 billion a year. Delta Air Lines (NYSE:DAL) is burning through "only" $12 million daily.

Cruise ship operators are also just barely treading water to stay afloat, with Carnival (NYSE:CCL) (NYSE:CUK), Norwegian Cruise Line Holdings (NYSE:NCLH), and Royal Caribbean (NYSE:RCL) all pushing their current relaunch dates further and further into 2021. Disney, too, recently canceled all spring cruises.

Even then, when they do take to the high seas once more, it will be with only a few vessels at greatly reduced capacity, hardly enough to sustain them for very long. It's not expected their flotillas will resume a full schedule until 2022 at the earliest, so new lockdown orders would push back their launch dates even longer, further endangering their ability to survive.

A glimmer of hope?

It could be that the economy will escape the devastation of new lockdowns if the vaccines being distributed prove fairly effective against the new COVID-19 strains, as some of the pharmaceutical companies and biotechs indicate they are.

Yet the threat of persistent lockdowns hanging over business is a danger investors need to remain cognizant of. Shutting down broad swaths of industry again will ruin the economy, regardless of whatever loans and assistance the government promises, sending the country into a new recession, if not depression.

With that possibility in mind, investors should assume a defensive posture and protect their portfolios from becoming encumbered by lockdowns.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.