Health experts have long been concerned about a potential "twindemic" of rising Covid-19 and flu cases. But now, an early surge of severe respiratory syncytial virus (RSV) cases among children is overwhelming hospitals nationwide, prompting worries of a "tripledemic."

Covid-19 and flu cases on the rise

As of now, Covid-19 cases are relatively low, but experts are concerned about the rise of certain omicron variants that appear to be better at evading immunity from vaccines and infection than previous variants.

One of the variants, known as BQ.1.1, has already led to case surges in Europe. BQ.1.1 and a closely related variant, BQ.1, accounted for just 3% of cases in the United States two weeks ago but now account for around 11% of cases.

The most recent booster shots made by Pfizer-BioNTech and Moderna were designed to protect against the omicron variants prevalent this summer, but not for newer variants. However, according to Aubree Gordon, an epidemiologist at the University of Michigan, the boosters still raise overall antibody levels and should help protect against severe cases of Covid-19 and shorten the duration of the illness.

Most variants circulating right now don't appear to cause more severe cases of Covid-19 than earlier versions of the virus, according to experts. However, the trend toward new variants being more adept at evading immunity is likely to continue.

"Now things have shifted with the massive degree of immunity that people have against previous variants," said Cornelius Roemer, a computational biologist at the University of Basel.

Meanwhile, data from Australia and New Zealand—where the flu season typically runs between May and October—shows that flu cases started rising weeks earlier than normal and both case and hospitalization numbers were significantly higher, suggesting the same could happen in the United States.

According to Gordon, influenza rates among children in Nicaragua—which usually has one flu season in June and July and then another one in late fall—were higher than rates seen during the 2009 pandemic, and children were sicker on average than in the past. "We saw a lot of hospitalizations," Gordon said.

Data from CDC shows that around 3% of flu tests nationwide were coming back positive for flu as of Oct. 8, but in the Southeastern region of the United States, that rate is higher than 10% and in the South Central region, the rate is higher than 5%.

'We're in uncharted territory'

On top of rising Covid-19 and flu cases, hospitals are also seeing RSV cases increase throughout the United States. RSV is a respiratory virus that typically manifests with mild, cold-like symptoms in adults but can lead to pneumonia and bronchiolitis in young children and can be life-threatening to infants and young adults.

According to data from HHS, pediatric bed capacity nationwide is at the highest it's been in two years, with 71% of beds filled.

CDC data shows more than 4,000 RSV cases are being reported every day, which is similar to the most recent RSV surge that occurred in the summer of 2021.

Over the last few weeks, Connecticut Children's Hospital has been operating over capacity due to a surge of RSV patients and is in talks with the National Guard and the Federal Emergency Management Agency about setting up a tent outside their hospital.

"We just don't have as many critical care beds as we have adult critical care beds simply because we don't usually need them," said Juan Salazar, physician in chief at Connecticut Children's.

"Our traditional pediatric in-patient beds, we have three floors with 25 beds in each location, we can expand to 28. All of those were full this morning," he added.

And at Children's Hospital of Philadelphia (CHOP), volumes are "extremely high right now in primary care pediatricians' offices, in urgent care centers, in our emergency departments, as well as in our inpatient units," according to Ron Keren, CHOP's CMO. "It's causing a lot of strain on the system, and it's a phenomenon that's happening across the country."

Keren said CHOP has been operating at near-full capacity every day for the last few weeks, and the demand is primarily coming from children, especially infants who have developed bronchiolitis from RSV. Keren said he believes the surge is due to a lack of immunity in the patient population.

"I think it gets to this idea that some folks are calling 'an immunity debt,'" he said. "We think that that may be because during the pandemic, there were a few cohorts of infants born who, due to social distancing and masking, probably didn't get exposed to these respiratory viruses, including RSV, and so they were not able to build up an immune defense to RSV and other respiratory viruses, leaving them vulnerable now."

The surge in RSV cases has experts concerned about what this winter could look like, with RSV, Covid-19, and flu cases all on the rise.

"As of today, we are seeing equal numbers of Covid, flu, and RSV and that's really concerning because we are very early for flu and RSV activity," said Diego Hijano, a pediatric infectious disease specialist at St. Jude Children's Research Hospital. "It's going to be a rough winter."

"You've got this waning Covid immunity, coinciding with the impact of the flu coming along here, and RSV," said Andrew Read, an evolutionary microbiologist at Penn State University. "We're in uncharted territory here." (Mandavilli, New York Times, 10/23; DePeau-Wilson, MedPage Today, 10/21; Romo, NPR, 10/24; Choi, The Hill, 10/22; Masciadrelli/Carberg, WTNH, 10/24; Pezenik/Kindelan, ABC News, 10/20)