COVID cases are rising and winter is coming. Should shoppers expect another wave of grocery shortages?

Retailers and wholesalers have been stockpiling items that would be most coveted if customers must retreat to their homes again, and they are hopeful that shoppers will be less likely to hoard supplies this time around — reducing the strain on the system.

But supply chains take a long time to align with fast-moving shifts in customer demand. Some goods, including paper towels and cleaning products, still have not entirely caught up.

“There are still some items that we really cannot get,” said Michael Violette, chief executive of Associated Grocers of New England, a wholesale distribution center for the region’s independent grocers.

A resurgence of the virus could also disrupt production of products such as fresh produce and meat.

Nada R. Sanders, distinguished professor of supply chain management at Northeastern University, said the prospect of shortages remains considerable as Thanksgiving and the winter holidays approach.

“The level of panic may not be as much as it was in the spring, but I think the consumer demand will be as high through the holidays,” she said. “Once we are done with the holidays, we are going to start seeing a dip back to normalcy.”

Even if no crisis emerges this winter, the pandemic has already changed how grocers stock their stores, in ways that customers can expect to see for a long time.

The toilet paper panic of the spring seems to have mostly subsided. Retailers say they generally have enough on hand. Producers have been able to shift to making more toilet paper for the home, rather than commercial supplies for offices. Meanwhile, customers who bought in bulk earlier in the year have slowed down their purchases — allowing stocks to replenish.

But that doesn’t mean customers will be able to get as much as they want of their preferred brand whenever they like. Roche Bros. says its stores are still dealing with some out-of-stock items, and that could get worse as the holiday season approaches.

Demand for paper towels, in particular, has remained higher than usual, even after sales doubled in the early weeks of the pandemic.

Georgia-Pacific, the massive producer whose brands include Sparkle and Brawny, said people are buying 15 to 20 percent more than usual, which a spokesman said is “a big increase to absorb for an industry that is used to a very consistent demand.”

The increase may be linked to the sustained demand in other cleaning products, such as sanitizing wipes, which have remained hard to come by through the summer and into fall.

If you’re used to choosing between 45 flavors of salad dressing, or if you have an obscure favorite variety of canned stew, you may find it harder to find exactly what you want as the winter goes on.

Sanders, of Northeastern, said savvy store managers will devote their resources to accumulating as much as they can of the products people want most. That allows companies to limit how much money they have tied up in inventory, she said. And many manufacturers are cutting down on the varieties they produce.

Violette, of Associated Grocers of New England, said he is trying to keep a stable supply of products that will be popular over the holidays, particularly ingredients for baking. He has 15,000 cases of flour on hand, for example. That’s about as much as the organization sold from April to September, when sales of flour were up 218 percent over the comparable period in 2019.

Some grocers are also accumulating what are being called “pandemic pallets” ― including paper goods and cleaning supplies. And many have worked for months to be ready for the holidays.

“For folks wondering about turkeys for Thanksgiving and Christmas, we believe we’re well-positioned for the holidays. Orders for these meats are placed much earlier in the year, so these items are already in cold storage,” Jennifer Brogan, spokeswoman for Stop & Shop, said in an e-mail. “We have not only increased our buy, we have also shifted the focus into smaller turkey sizes, anticipating more small gatherings.”

But stocking up on inventory can be more of a challenge for smaller grocers with less room to store surplus goods. Chris Crosby, president of Crosby’s Marketplace, which has seven stores, mostly on the North Shore, said he is hopeful that holiday shoppers will pick up what they need early, to limit the rush and the strain on stocks.

“There might even be more people in the store who don’t usually shop. They might go to a relative’s place. So that puts more pressure on us, too,” Crosby said.

While grocers have had some success in stocking up on items that won’t spoil, the supply of perishables is more vulnerable to production disruptions.

Anna Nagurney, a professor who studies supply chain management at the University of Massachusetts Amherst, said she has some particular concerns about the supply of fresh produce — especially from international sources.

The pandemic has shaken up trade, with some countries trying to hang onto fresh foods, and others banning imports. International outbreaks could affect the availability of foods that are typically grown overseas in winter.

On top of that, Nagurney said, the supply of fresh foods grown or processed in the United States can be affected by the virus. This spring, shutdowns at meat-processing plants created shortages in that industry.

“Without people, we don’t produce anything,” Nagurney said.

Crosby said that even at the height of the meat processing slowdown, customers' reaction to the prospect of shortages was a major reason things went out of stock. “Once people start to panic, it starts that problem going.”

While a lot remains uncertain, there is one big advantage that our food system did not have in the spring: experience with a pandemic. There’s better science, albeit imperfect, about how to control the virus.

In the spring, Sanders said, “there was this fear that grocery stores, everything, entire cities will be shut down. That is not going to happen under any circumstances.”

Andy Rosen can be reached at andrew.rosen@globe.com.