Respiratory syncytial virus (RSV)

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Data from a large cohort study suggest there have been changes in the seasonal timing of respiratory syncytial virus (RSV) and bronchiolitis infections since the COVID-19 pandemic—particularly as it relates to hospitalizations among older children with RSV—but that some of this change may be driven by an increase in overall testing practices.¹ The data point toward a need for novel prevention strategies in this affected pediatric population.

All told, the study incorporated data from 2015 to 2022 that included a total of 924,061 patient cases collected from (RSV: 348,077; bronchiolitis: 575,984; median age, 8 months [IQR, 5-16]; 42% female), and identified that the peak of the RSV season occurred much earlier in the year in 2022 compared with 2023 than what pre-2020 numbers indicate. In 2022, it ran from September to November, whereas in 2023, when it ran from December to January.

This, the investigators noted, signaled an “an overall shift in RSV seasonality toward a summer season in 2021. Although seasonal timing began to shift back to a more typical pattern (eg, occurring in colder months) in 2022 to early 2023, the number of cases in children younger than 5 years was higher overall during this season.”

The data were published in JAMA Network Open by Robert J. Suss, MPH, and Eric A. F. Simões, MBBS, DCH, MD, both of the Department of Pediatric Infectious Diseases at the University of Colorado School of Medicine and Children’s Hospital Colorado, the latter of whom also works in the Colorado School of Public Health’s Center for Global Health in the Department of Epidemiology. RSV testing, they noted, seems to have increased from the 2015-to-2019–time frame to the 2020-to-2022–time frame—17% of the 425433 non-RSV bronchiolitis patients (n = 72,428) were tested for RSV in the former period compared with 25% of the 150,019 patients (n = 37,535) in the latter period.

Overall, there was an increased incidence of RSV and a decreased incidence of non-RSV bronchiolitis across the age groups and care units examined in 2021 and 2022 compared with 2015 to 2019, with a few exceptions. Of the 348,077 RSV cases, hospitalization occurred in 54% (n = 187,850), and a higher proportion of patients with RSV were admitted to the ICU, at 19.7% (n = 68,550) than bronchiolitis, at 8.6% (n = 49,560).

READ MORE: Pfizer Abrysvo RSV Vaccine Meets Primary Endpoints for Adults Ages 18 to 59

Incidence rate ratios (IRRs) of hospitalization increased for all ages in 2021 and 2022 compared with the 2015-to-2019–time frame, with those aged 24 to 59 months being 4.86 times (95% CI, 4.75-4.98) as likely to be hospitalized in 2022 compared with 2015 to 2019, and those aged 12 to 23 months were 3.90 times as likely (95% CI, 3.81-3.98). Infants, aged 0 to 5 months, were 1.77 times (95% CI, 1.74-1.80) as likely to be hospitalized, and those on Medicaid had an increased likelihood compared with non-Medicaid patients, regardless of the year.

“Infants may have had less exposure to RSV during the COVID-19 pandemic in 2020 to 2021, which may have increased the susceptibility of those 12 months or older during 2021 to 2022,” Suss and Simões wrote, adding that they, “speculate that some of this is due to the increased testing observed among the non-RSV bronchiolitis cohort; the finding that the IRRs in this cohort were generally less than 1 suggests an increase in RSV test positivity.” Of note, though, they mention, however, that emergency departments (EDs) showed lower rates of use in patients up to 23 months of age. Comparatively, though, the 24-to-59–month group saw a 1.7- to 2.0-fold higher ED use in 2021 and 2022.

Suss and Simões pointed to several strengths of the analysis, including the larger sample sizes because of available national data, which led to more precise stratification of the findings. Similarly, the completeness of ICD code data allowed for more clear distinction between diagnoses, which “could have been differentially impacted by increased testing for RSV after the COVID-19 pandemic. If this is the case, the combined data may provide a more accurate estimate of the probable burden of RSV.” As for limitations, they did note that the data rely on a relative assumption of steadiness of the US population between 2015 and 2022, which also assumes that the PHIS hospitals included had comparable frequencies to prior data collected by Rha et al in 2020;² and that population risk was considered to be the total estimated population under the age of 5, to allow for incidence approximations by care unit between those on Medicaid vs private insurance.

“This study found that the burden of RSV and related non-RSV bronchiolitis HCRU increased in 2021 and almost doubled in 2022 (except for ED use in the non-RSV and combined cohorts, which decreased) after a decrease during the pandemic in 2020. Older children had absolute increases in [healthcare resource utilization] and disease severity, regardless of increases in testing in that population,” Suss and Simões concluded. “This finding has implications for newly available prevention strategies (eg, monoclonal antibodies), for which older children are not currently eligible.”

What Clinicians are Witnessing in Terms of RSV Incidence

Last year’s historic RSV season left many wondering if this was going to become a recurring trend, driving the research such as that done by Suss and Simões. In the below segment of our RSV Rountable Series—a collaborative effort from Contemporary Pediatrics, Contagion, and Contemporary OB/GYN—physicians with various areas of expertise weigh in on what they are seeing at their institutions in terms of infection rates.

References
1. Respiratory Syncytial Virus Hospital-Based Burden of Disease in Children Younger Than 5 Years, 2015-2022. JAMA Netw Open. 2024;7(4):e247125. doi:10.1001/jamanetworkopen.2024.7125
2. Rha B, Curns AT, Lively JY, et al. Respiratory syncytial virus-associated hospitalizations among young children: 2015-2016. Pediatrics. 2020;146(1):e20193611. doi:10.1542/peds.2019-3611