What we learned from the Covid-19, flu, and RSV tripledemic

The triple threat of influenza, respiratory syncytial virus (or RSV), and Covid-19 have been another stress test for the broken US health care system this winter. But after the success of the wave, it seems to be letting up, at least for now.

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

Influenza activity nationwide has also been on the decline for several weeks, based on positive test results reported to the CDC. Hospitalization rates for the flu have declined since cresting in December, shortly after an initial surge in activity.

RSV kicked off this cold and flu season, with hospitalizations in mid-November at twice the rate seen in the most recent pre-pandemic RSV season, before stopping. Experts were struck by the dramatic early onset of illness, compared to pre-Covid norms, and warned of flu and Covid surges to follow.

That has now come and gone, although people are still sick and some hospitals remain strapped for staff and resources after three difficult years. There is also the possibility of a second wave of influenza, experts say, if another strain of the virus emerges and begins to spread widely, something that can happen and has happened in previous flu seasons.

But if not, this worst respiratory virus season may be over. Three successive peaks and troughs, packed into three months. I asked what the experts made of this experience, as we together became the new normal. The federal government is considering how to prepare the annual Covid-19 vaccine. US hospitals are still adjusting to what they describe as a period of near-permanent crisis.

With the novel coronavirus no longer novel, but a tool of the viral ecosystem, we’re trying to figure out what to expect and what other respiratory viruses compete with each year as temperatures drop.

It’s a work in progress — and experts’ reflections on this strange cold, flu, Covid, and RSV season reflect a viral world in transition. Here’s what they learned, and what they can tell about the disease in the future.

1) Influenza and RSV can spread easily after a few slow years

RSV has been behaving strangely, with an unusual summer spike indicating the start of an equally unusual winter wave. This year’s peak is almost two months earlier than the 2019-2020 season, the last “normal” season before Covid-19 appeared.

This year is also more severe, with peak hospitalization rates nearly doubling in 2019-2020. Most experts attribute the timing and severity of this year’s RSV and flu season to less exposure to people after the past two years when masking and social distancing were more common. Children, who are usually vectors for the spread of the virus, in particular do not have much chance of catching and spreading the disease until this year.

“This flu season started so early because there are so many kids who don’t have the flu, the common cold, and RSV,” said David Celantano, chair of epidemiology at Johns Hopkins.

This season there has been a lot of flu and even RSV among the more susceptible adults. People of all ages have generally been less affected by the disease for several years now. Due to the increased level of immunity of the population to Covid-19 after the brutal pandemic, it is easier for other viruses that have been inactive to be contained.

2) New variants have caused the continued spread of Covid-19

Covid is experiencing a third winter wave, after influenza and RSV have ripped through the population. This year’s surge in cold weather is smaller than the peak of America’s pandemic, in January 2021, with about a quarter of cases and a third of hospitalizations, according to New York Times trackers.

The coronavirus is the opposite of its viral competitors: Most Americans have had it at least once in the past few years and probably more, and most have been vaccinated at least once or twice. The booster shot designed for the omicron variant has given the recipient an additional layer of protection.

All that built-up immunity may explain the relatively mild winter spike, experts say, even though we’ve paid a heavy price to get to this point, with more than 1.1 million Americans dying, and more than 500 more dying every year. average day.

And Covid-19 continues to find ways to take advantage and continue to spread. While the spread of RSV and influenza can be attributed to a weakened immune system, SARS-Cov-2 is still evolving rapidly. Monica Gandhi, an infectious disease expert at the University of California San Francisco, examined more than a dozen variants, from BA2 to XBB1.5, that had spread in the last phase of the pandemic.

“The rise with Covid is related to the appearance of variants that are more transmissible,” said Amesh Adalja, a John Hopkins infectious disease physician, “as opposed to what happened with influenza and RSV.”

Pre-existing immunity should continue to reduce the likelihood of severe disease for most people, although the elderly and immunocompromised are still at higher risk than others. The FDA recently limited plans to have people receive annual booster shots, primarily as a way to protect the population.

“The fact that immunity to Covid has been built into the population (at a cost, it must be said) bodes well for future prospects,” said Josh Michaud, an infectious disease expert at the Kaiser Family Foundation. “But exactly how next season or the coming months will be is still difficult to know.”

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

Infectious disease experts know this year could be even more extraordinary. Covid-19 has been the biggest disruption to normal disease cycles in a century, and we know from previous experience that major pandemics can be followed by chaotic viral behavior for a year or two before settling into a more normal pattern. This happened with the 1918 flu and the 2009 H1N1 pandemic.

For RSV and influenza, the past two years have been aberrations; it is reasonable to expect a more normal pattern will continue in the future as immunity rebuilds. (However, every cold-and-flu season will be different — variations from season to season remain.)

“I think this is only temporary and it will all become a more regular pattern in the coming season as the typical population immunity returns,” said Richard Webby, an infectious disease researcher at St. John’s Children’s Research Hospital. Jude.

Covid-19 is more difficult to project, as it is constantly evolving to become more transmissible. So far, protection from infection and previous vaccines appear to be effective for most people, at least in preventing hospital stays. But it also continues to be a threat to the unvaccinated, the elderly, and the immunocompromised – and it increases every year when conditions are better for the spread of the virus (ie, winter).

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

Experts also advise us to be careful, because Covid is a virus that we are not familiar with 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 forward, but the story of the pandemic is far from over.

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