This Year’s RSV Surge: Bigger, Earlier, and Older Than Previous Seasonal Outbreaks

Respiratory syncytial virus (RSV) manifested earlier and in significantly higher numbers at the outset of the 2022-2023 viral season, with hospitalizations climbing to a high of 4.9 per 100,000 in mid-November — a sharp rise from last year’s mid-November hospitalization rate of 1.1 per 100,000 and pre-pandemic rates of roughly 0.5 per 100,000.^1.2 Although RSV numbers began to fall during late November, RSV detection and hospitalization rates still remain higher than in previous years,^1.2 and certain features of this season’s outbreak clearly set it apart from previous years. 

Unprecedented Surge in Cases

Pediatric hospitals have been overflowing with children with RSV, far in excess of the peaks we saw during the pandemic or during a typical surge year, according to Chris Carroll, MD, FCCP, a pediatrician and Chair of the Critical Care Network at the American College of Chest Physicians. “Every 2-3 years, there is a severe viral season where we see more children in the hospital with RSV than a typical year.” However, the recent surge of patient admissions was “several-fold higher than in even such a surge year,” added Dr. Carroll, who said his colleagues nationwide have seen “2 to 4 times the number of children that we would see during a typical surge year.”

Respiratory syncytial virus is a common cause of respiratory infection for which there is no FDA-approved vaccine. In most people, its effects are limited to cold-like symptoms. However, in the very young (ie, children under 5 years old) and in older adults — especially in those with cardiac, pulmonary, and neuromuscular comorbidities and/or low immune function — the virus may cause severe consequences, such as pneumonia and bronchiolitis. In a typical year, RSV results in 60,000 to 120,000 hospitalizations among adults 65 and over, with 6,000 to 10,000 deaths, and sends 58,000 to 80,000 children 5 years or younger to the hospital, causing 100 to 300 deaths in that age group.³

Children have been most visibly affected by this year’s spike in RSV; the hospitalization rate during the early months of winter for children aged 0 to 4 years rose to 61.5 per 100,000 in mid-November, substantially higher than last year’s early winter peak of 13.3 per 100,000 on December 11, 2021. Although hospitalizations for children 0 to 4 years of age dropped to 17.9 per 100,000 as of November 26, 2022, that rate still outpaces the rate for approximately the same time last year.²

Rates of hospitalization for patients aged 65 and older are much lower but nevertheless follow similar trends to those of young children. In 2022, hospitalization rates for adults older than 65 years of age rose to an early winter peak of 3.6 per 100,000 in mid-November. Notably, this is higher than the 2021 early winter peak of 2.3 per 100,000 reported December 11, 2021. Moreover, although current rates of hospitalization for older adult have come down (to 2.7 per 100,000 as of November 26), those rates are nevertheless higher than for approximately the same time last year.²

Older Children

The age of patients affected by this year’s RSV outbreak further sets this season apart from past seasons. In the past, young children presented to hospitals in large numbers, but this year children over 5 are being hospitalized far in excess of their numbers in previous seasons.  As of mid-November, the rate of hospitalizations for RSV of children aged 6 to 17 reached an early winter peak of 2.2 per 100,000 — compared with last year’s early winter peak of 0.3 per 100,000 on December 11, 2022. (Notably, as of November 26, 2023, the hospitalization rates for this age group dropped to 0.5 per 100,000).²

Why the increase in RSV hospitalization rates in older children? As Dr Tan explained, “During the COVID-19 pandemic, there were quarantine and isolation at home. After that there were mask mandates and other protective mitigation protocols. Fewer of the kids who were either infants or young children during the pandemic were exposed to RSV like they normally would be. Now those kids are older, and are finally being exposed to RSV, and are getting actually fairly ill with it when they get the RSV.”

Similarly, older adults who were isolated or wearing masks frequently were generally not exposed to RSV during the early phases of the COVID-19 pandemic. Now those older adults, especially those with compromised immune function, are facing more serious infection with RSV later in life or with fewer biological defenses.

Timing of Post Pandemic RSV Outbreaks

Since the onset of COVID-19 pandemic, not only are more people than usual being affected by RSV; the seasonal timing of RSV has also changed.³ RSV typically begins to rise in September, peaking between December and February. But in 2021, RSV cases instead began to increase during the spring, peaking in July. This year, cases again rose during the late spring and summer.

The reason for this altered timing is unclear. “It’s been theorized⁴ that this could have been caused by some viral kind of interaction between the different viruses,” said Tina Q. Tan, MD, Professor of Pediatrics and an attending physician in pediatric infectious diseases at the Feinberg School of Medicine, Northwestern University. “Because COVID-19 was such a predominant virus it may have limited the amount of RSV and flu that were in circulation. But now COVID has changed somewhat — it’s not the same variants and subvariants. And with the lifting of mask mandates and other protective protocols, more people are being exposed to many other individuals, so that these viruses are now being transmitted and causing the amount of disease that we’re seeing.”

Will There Be a “Tripledemic” This Winter?

The combination of the influx of RSV, the ongoing COVID-19 pandemic, and an influenza season anticipated to be severe has been referred to as a “tripledemic.” Notably, the potential for a tripledemic this winter may potentially raise both the magnitude and complexity of the current RSV outbreak. In fact, Dr Tan speculated that we are already seeing the combined effects of these respiratory illnesses. “In addition to individuals that have only RSV, there are some areas of the US where flu is circulating at very, very high levels, and they also have RSV. And COVID is also still circulating, and the number of people being hospitalized for COVID-related complications is starting to increase again in some areas of the United States. So it’s a combination of all these viruses that is really driving the increased number of people who require hospitalization.”

The specter of a tripledemic has raised concerns regarding the consequent strain on health care systems, including overwhelmed bed capacities and clinician burnout. Dr Carroll warned, “The pediatric community is not seeing a widespread surge in COVID right now.  But if influenza follows historical patterns, we expect it to peak in the coming months. This could extend the current surge in cases and a crisis in pediatric hospitals through the spring. If that happens, there could be delays in care and increased burnout of staff.” Dr Tan added that such strain could also affect adult ICUs.

Education for those at risk for RSV and their families may potentially ease the strain of increased RSV on health care systems and prevent excess deaths. As Dr Carroll advised, “The best way clinicians can respond to this increase is to educate families on what to look for when their child is ill. Children who seem like they are struggling to breathe, who have noisy breathing or expiratory grunting, or who are abnormally sleepy and difficult to awaken, should be evaluated by a clinician. Clinicians should also advise parents and families to keep their infants and toddlers away from those who are sick.” Dr Tan suggested that people headed for indoor gatherings or in contact with large numbers of people should be advised to wear a face mask.

Drs Carroll and Tan both emphasized the importance of clinicians urging their patients to receive influenza vaccinations and COVID-19 boosters. The more people who are vaccinated, the less likely it is that those who are at-risk will be exposed to those viruses. Physicians and nurses also should recommend immunization against other vaccine-preventable diseases that tend to circulate during the winter, such as pneumococcal pneumonia and pertussis.

Such patient education and vaccination efforts are crucial to avoid the sort of overload that health care systems have faced in the past couple of years, Dr Tan said. “Yes, there are contingency planning efforts that hospitals are working on, to really try and maximize the number of beds that they’re able to staff in order to provide care. But what we saw with the first wave of the pandemic, where health care systems were completely strained and overloaded — that’s what we’re trying to prevent.”

Dislosure: Dr Tan is a member of the vaccine advisory boards of Merck, Sanofi Pasteur, GSK and Pfizer/Wyeth.

This article originally appeared on Pulmonology Advisor