Pandemic precautions made for an illness-free year for many. What that means for our immune systems.

For all the horrors of our pandemic year, many of us now in our fifth season of working from home, keeping our six-foot distance, scrubbing our hands and wearing masks during our rare shopping trips have reaped one fantastic benefit.

We haven’t been sick for ages. It’s glorious.

But now what?

We’re not there yet, but the day is coming when some combination of vaccines and natural immunity will bring COVID-19 cases way down — at least in communities with high vaccination rates. “Normal” life will be a legit possibility.

And all those other viruses and bacteria we haven’t been getting this last year will be out there waiting for us to let down our guard. Are we going to try to keep this winning streak going by wearing masks even if the CDC says it’s OK not to? Would it be bad for our immune systems to keep avoiding germs? Do kids need those germs more than adults?

We posed these questions and more to immunologists and other physicians. As with most COVID-19-related questions, there’s much that doctors don’t yet know. The immune system is immensely complicated, and we’ve never had a year like this one, but doctors had some interesting educated guesses.

Since early last year, the coronavirus has infected at least 31 million people in the United States and killed more than 564,000, according to Johns Hopkins University. Meanwhile, doctors said, it is clear that other viruses have been in retreat. There have been fewer cases of rhinovirus, a common cause of colds, and of respiratory syncytial virus (RSV), another illness that can be severe for babies and seniors. Flu practically flat-lined in a year when many experts feared a “twindemic” of influenza and COVID-19.

» READ MORE: RSV, the other virus that kills during flu season

So far this flu season — the season officially ends May 22 — there has been only one pediatric flu death in the country, according to the U.S. Centers for Disease Control and Prevention. Compare that with 144 to 198 during each of the previous three years. Pennsylvania has had only 3,351 lab-confirmed cases this season. There were more than 131,000 during the 2019-2020 season and nearly 100,000 during the previous season.

“This is an unprecedented moment,” said Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia. “This year, flu is gone.”

» READ MORE: Flu and other infections are down, likely due to COVID-19 social distancing

William Schaffner, an infectious-diseases specialist at Vanderbilt University Medical Center, thinks the fact that most kids, who are major flu spreaders, were in virtual school was a prime factor.

There has been so little flu that some doctors worry it will be hard to accurately predict which strains will circulate in the fall. Those predictions, which are used to produce flu vaccines, are usually based on flu cases in the southern hemisphere.

Offit, who is on the Food and Drug Administration committee that made the flu-shot decision in March, thinks the committee had enough information.

Regardless, flu and other winter viruses will likely be back this year as schools and businesses transition from virtual to in-person life, Offit said.

Does that mean our bodies could really get slammed now that our immune systems are out of practice? Perhaps you’ve heard of the hygiene hypothesis, a theory that posits that early exposure to microbes and animals is good for our immune systems. It stemmed from the observation that people raised on farms are less likely to develop asthma and allergies than those who spent childhood in cleaner environments.

One correlate of this theory is that our immune systems need exposure to pathogens to develop properly. Another, said E. John Wherry, a Penn Medicine immunologist, is that people with allergies and asthma may get sicker when infected with respiratory viruses.

Several doctors said this theory is complex and imperfect, but they believe there’s some truth to it. However, they saw no downside to adults taking a long break from infections. Most of us have decades of experience with common germs, and our immune systems have long memories.

“Our immune system has been well-primed over years,” Schaffner said. “We’re not two or three years old.”

» READ MORE: New parents worry how pandemic isolation will delay infant development: ‘I’m trying not to spiral downhill’

Sandra Gawchik, an allergist and immunologist at Asthma & Allergy Associates in Delaware County, agreed. The immune system develops in children until they’re about 6, she said, but “adults already have a fully developed immune system.”

Wherry said it’s probably fine for adult immune systems to rest. “This is not like going to the gym [where] if you stop lifting weights, you’re going to get weaker,” he said.

On the other hand, he said, frequent infections, which can lead to chronic inflammation, weaken your immune system’s response to a new invader. He likened it to asking a marathon runner to sprint after the 16th mile.

It is possible, though, that infection with one germ might protect against another. Wherry said there’s some evidence that people with latent tuberculosis infections are less likely to get the coronavirus. A 2020 Yale University analysis found that infection with rhinovirus interfered with spread of an emerging strain of influenza A in 2009. However, Wherry said, there’s no reason to think that infection with the usual random winter germs will protect against new germs such as COVID-19.

More important, no amount of precaution completely protects us from invasion. There are still germs on our food, on our pets, in our gardens. Our immune systems are working every day.

John Russell, chair of the department of family and community medicine at Abington-Jefferson Health, thinks the decrease in social activity could reduce the diversity of our microbiomes, the vast society of bacteria that lives in our guts. The microbiome, he said, interacts with our immune system. “All of this stuff is conjecture,” he said, “but certainly it’s a little bit of a possibility.”

The best way to strengthen your immune system, Wherry said, is to take care of yourself. Eat a healthy, varied diet. Exercise. Get enough sleep.

» READ MORE: How to keep your immune system healthy during the coronavirus pandemic

The situation with kids is a little murkier. Doctors believe their immune systems do need challenges to learn to work well. “I do think that there’s some sort of priming that’s necessary for young children,” said John Zurlo, an infectious-diseases doctor at Jefferson Health. This is not an argument against vaccination. There are plenty of other germs that can do the job.

However, doctors don’t see a short break as problematic and said that kids who play outside are still getting exposures.

Doctors expect that the pandemic will — should — lead to some long-lasting changes in behavior.

“I think it’s going to take a while before people become so carefree with regard to infectious disease,” Russell said.

Better hand washing was always a good idea, so keep it up. There’s no reason not to continue to wear masks, especially in crowds. People in Asian countries have long worn masks in public, especially when they felt sick.

“I think it’s a good idea if you’re sick that you wear a mask, so you don’t infect other people,” Gawchik said. Masks can also reduce allergy symptoms.

You may see doctors and nurses wearing masks more often even after COVID-19 levels are low and vaccination levels are high. “I just wonder whether masks are here to stay during flu season for health-care workers,” Zurlo said.

Robert Finberg, an infectious-diseases doctor and immunologist at University of Massachusetts Medical School, said doctors and nurses now realize what a difference masking makes. Before, he said, “we didn’t believe it works as well as it seems to.”

Now that we’ve also learned how well many can work from home, some hope that the pandemic will reduce another source of disease spread: the office martyr who comes to work sick and breathes on colleagues all day. Wherry expects that person will face much more intense push-back than in the past. Coworkers might say, “That’s really rude. What are you thinking? Why are you here?”