The triple threat of influenza, respiratory syncytial virus (or RSV), and Covid-19 has been another stress test for a battered US health care system this winter. But after a succession of waves, it seems that it’s letting up, at least for now.

After a notable increase in hospitalizations began in late November, this winter’s Covid-19 wave appears to have peaked earlier this month, with hospitalizations and deaths now down 25 percent and 1 percent respectively over the past two weeks. (The US is also reporting fewer cases, down from an average of about 65,000 new cases every day to about 46,000 daily cases now, but case data has become less reliable with the prevalence of at-home testing.)

Influenza activity nationwide has also been steadily declining for several weeks, based on positive test results reported to the CDC. The hospitalization rate for the flu has been dropping since cresting in December, shortly after the initial surge in activity.

RSV kickstarted this cold-and-flu season, with hospitalizations peaking in mid-November at twice the levels seen in the most recent pre-pandemic RSV season, before dropping off. Experts were struck then by the early, dramatic increase in illness, compared to what had generally been the pre-Covid norm, and warned of the flu and Covid surges to follow.

Those have now come and gone, though people are still getting sick and some hospitals remain strapped for staff and resources after three difficult years. There also remains the possibility of a second influenza wave, experts say, if another strain of the virus emerges and starts spreading widely, something that can happen and has happened in previous flu seasons.

But if not, the worst of this strange respiratory virus season may have passed. Three successive surges and peaks, packed into three months. I asked what experts made of this experience, as we collectively settle into a true new normal. The federal government is considering how to set up annual Covid-19 vaccines. US hospitals are still adjusting to what they describe as a period of permanent near-crisis.

With the novel coronavirus no longer novel, but a fixture of our viral ecosystem, we are trying to figure out what to expect from it and the other respiratory viruses it is competing with every year when temperatures drop.

That is a work in progress — and experts’ reflections on this weird cold, flu, Covid, and RSV season painted a picture of a viral world in transition. Here’s what they learned, and what it might tell us about illnesses in the future.

1) Influenza and RSV were able to spread easily after a couple slow years

RSV had already been behaving strangely, with an unusual summer spike presaging an equally unusual early start to its winter wave. This year’s peak arrived almost two months earlier than in the 2019-2020 season, the last “normal” season before Covid-19 appeared.

This year was also much more severe, with a peak hospitalization rate that nearly doubled the 2019-2020 high. Experts generally attribute the timing and the seriousness of this year’s RSV and flu seasons to people’s lack of exposure after the past two years when masking and social distancing were more common. Children, who are typically vectors for viral spread, especially had not had as many chances to catch and spread diseases until this year.

“This flu season started really early because there were so many children with zero experience with flu, common colds, and RSV,” David Celantano, chair of epidemiology at Johns Hopkins, told me.

This season has seen a lot of flu and even RSV among more vulnerable adults. People of all ages have generally been less exposed to disease for a few years now. Given the growing level of population immunity to Covid-19 after a brutal pandemic, it was easier for the other viruses that had been lying dormant to take hold.

2) New variants have been driving Covid-19’s continued spread

Covid experienced its third winter wave, after influenza and RSV had ripped through the population. This year’s cold-weather surge has been substantially smaller than what was the peak of America’s pandemic, January 2021, with about a quarter of the cases and a third of the hospitalizations, per the New York Times’s tracker.

The coronavirus was the opposite of its viral competitors: Most Americans have been exposed to it at least once in the past few years and maybe multiple times, and most of them have been vaccinated at least once or twice as well. Booster shots designed for the omicron variant have given the people who got them an additional layer of protection.

All of that built-up immunity likely explains the comparatively mild winter surge, experts say, though we have paid a high price to reach this point, with more than 1.1 million Americans dead, and more than 500 people still dying every day on average.

And Covid-19 has continued to find ways to gain an advantage and continue spreading. While RSV and influenza spread can be attributed to dormant immunity, SARS-Cov-2 is still evolving quickly. Monica Gandhi, an infectious disease expert at the University of California San Francisco, ticked through more than a dozen variants, from BA2 to XBB1.5, that have been circulating in the later phases of the pandemic.

“The ups and downs with Covid are related to the appearance of more transmissible variants,” Amesh Adalja, a John Hopkins infectious disease doctor, said, “versus what happened with influenza and RSV.”

The preexisting immunity should continue to lower the likelihood of severe disease for most people, though the elderly and immunocompromised are still at higher risk than others. The FDA has recently outlined its plan for people to receive annual booster shots, particularly as a way of protecting that population.

“The fact that immunity to Covid has been built up in the population (at a cost, it must be said) is good for future prospects,” Josh Michaud, infectious disease expert at the Kaiser Family Foundation, told me. “But exactly how next season or even the coming months play out is still hard to know.”

3) We are still in a post-pandemic transition phase for respiratory viruses

Infectious disease experts knew this year might be an outlier. Covid-19 has been the biggest disruption to the normal cycle of disease in a century, and we know from prior experience that major pandemics can be followed by a year or two of chaotic viral behavior before settling into a more normal pattern. It happened with both the 1918 flu and the 2009 H1N1 pandemic.

For RSV and influenza, the past two years have been aberrations; it is reasonable to expect more normal patterns will resume in the future as immunity builds back up. (Still, every cold-and-flu season will be different — variation from season to season is a constant.)

“My guess is that this is entirely temporary and things will settle down into more routine patterns in coming seasons as typical population immunity gets back on track,” said Richard Webby, an infectious disease researcher at St. Jude Children’s Research Hospital.

Covid-19 is trickier to project, given its continuing evolution toward more transmissibility. So far, the protection from prior infection and vaccines seems to be effective for most people, at least in preventing them from ending up in the hospital. But it also continues to pose a threat to the unvaccinated, the elderly, and the immunocompromised — and yearly surges when the conditions are more favorable for viral spread (i.e., the winter) are to be expected.

“I would expect RSV and flu to be more like normal next year,” Bill Hanage, a Harvard University epidemiologist, told me. “Covid, it remains to be seen, but a peak in early January 2024 is almost certain.”

Experts also advised caution, as Covid is a virus we simply do not have the same familiarity with as, say, the flu virus, and it is still reaching some parts of the world (most importantly China) for the first time. Normal life in the United States may be moving on, but the pandemic’s story isn’t over yet.

“Are we past the worst? Probably,” Celentano said. “But I am not a betting man!”