Why are so many people sick right now?

(NEXSTAR) – One week after the Thanksgiving holiday, and chances are good that you are sniffling, coughing or feeling a little scratch in your throat. It’s not just you – the country is contending with a “tripledemic” of viruses (not to mention, a whole lot of common cold).

As of late November, reported COVID-19 cases in the U.S. were stable, but high. The Centers for Disease Control and Prevention recorded about 300,000 new cases over the past week, but that number is likely an undercount, as home tests often aren’t reported to public health agencies.

Meanwhile, influenza is rising rapidly and on its way to a peak much earlier than the typical flu season. The CDC’s preliminary count is rough, but the agency believes as many as 14 million have been sickened and up to 8,400 people have died.

This year’s influenza season has also been especially hard on children, as has RSV (respiratory syncytial virus). RSV has had children’s hospitals around the country overflowing or at capacity since October.

What’s behind the seemingly omnipresent illness? Is it that there are suddenly more viruses than there were before? Or is it that our immune systems are weaker after years of masks and social distancing?

According to Dr. Andy Pekosz, a virologist and professor at Johns Hopkins Bloomberg School of Public Health, it’s neither.

“It’s not that our immune systems are weaker, because it certainly seems like everybody is recovering. There’s not a really high increase in, let’s say, the mortality rate with the flu so far,” he explained.

If our immune systems had collectively weakened since 2020, we’d expect to see people getting sicker and dying more frequently from influenza, RSV or COVID-19, but that’s not the case. It’s more likely that we’re just “seeing the effects of three years of lack of virus circulation,” Pekosz said.

RSV, for example, is a common virus we’re exposed to regularly. It’s usually hardest on young children and babies, who haven’t built up immunity from repeated exposures. This year, adults are getting it a lot, too.

“People have not been exposed to RSV as much, so their bodies have likely stopped making the antibodies,” Dr. Jim Scott, Dean of Touro University California College of Pharmacy, told Nexstar’s KRON. It’s not that our immune systems forgot how to create the necessary antibodies, but it just takes some time for antibody production to “ramp up and meet the need.”

Staying home, masking and avoiding large gatherings wasn’t just effective at curbing the spread of COVID – it also brought the levels of flu transmission and other respiratory viruses way down. Pretty much all of those measures have been lifted, and viruses have started spreading rapidly again.

“It’s a normal process that we see here. It’s just that without seeing it for three years, we now have this large bounce back to bring us back to equilibrium,” Pekosz said.