The Frequency of Hospitalizations for RSV and Influenza Among Children and Adults: An Analysis From the Years 2016–2022

By the end of 2022, a massive wave of infections saw children‘s hospitals in Germany and the entire Northern Hemisphere stretched to or beyond maximum capacity (1). There has been some debate in this context as to whether the COVID-19 pandemic has made children more vulnerable to pathogens such as human respiratory syncytial virus (RSV) (2) or influenza. In this discussion, it is helpful to extend the period analyzed to include the time before the pandemic and the situation among adults. With such an approach, the extent of the problem can be more accurately assessed, also for the future.

In our Children’s University Hospital at the Klinik St. Hedwig and the Krankenhaus der Barmherzigen Brüder Regensburg (both maximum-care hospitals/level 1 centers), regular polymerase chain reaction (PCR)-based RSV and influenza testing has been performed since 2016 in all patients with typical symptoms of viral infection (respiratory symptoms such as respiratory insufficiency and oxygen requirement, high fever or febrile seizures, in infants also refusal to drink in case of upper respiratory tract infection), using a uniform method (GeneXpert, Cepheid, Sunnyvale, CA, USA) (3). We systematically analyzed these data for a temporal assessment.

We included all patients hospitalized between August 2016 and February 2023 for symptoms characteristic of RSV/influenza with positive PCR test result (N = 3124, consisting of 2067 children and 1147 adults). RSV was detected in 1458 children (mean age 0 years; SD 3.6) and influenza in 635 children (mean age 3 years; SD 7.9); 26 children had dual infection with RSV and influenza. In 448 hospitalized adult patients with typical symptoms (mean age 77 years; SD 13.7) RSV was detected, in 709 patients (mean age 75 years, SD 16.2) influenza and in 10 cases both pathogens.

RSV- and influenza-related hospitalizations show a seasonal pattern in both age groups and a trend toward increased hospitalizations across the entire study period (Figure a, b). For RSV, an annual rhythm alternating between a high-prevalence season and a low-prevalence period season was found in both age groups, while for influenza this phenomenon was observed only among adults. During the COVID-19 pandemic, there were no cases of hospitalizations for RSV or influenza in the 2020/2021 season. In 2021/2022, there was a—considerably too early—re-occurrence of an RSV wave in children, and the 2022/2023 RSV season also started earlier. Unlike RSV, influenza-related hospitalizations continued to be sporadic in both age groups in 2021/2022. Waves of hospitalizations for influenza were observed again in both age groups in 2022/2023.

Figure a

Children hospitalized for RSV and influenza, 2016–2023 (cases per month)

Figure b

Adults hospitalized for RSV and influenza, 2016–2023 (cases per months)

It is very likely that the implementation and phasing out of pandemic-related infection control measures is the reason for the virtual absence of RSV- and influenza-related hospitalization waves during and after the COVID-19 pandemic and the significant shift in seasonality. When in 2021 the protective measure were lifted in children, RSV initially re-emerged in this age group, causing numerous hospitalizations. There were only sporadic RSV-related hospitalizations in adults during the 2021 season, which may be explained by the fact that in that year protective measures continued to be in place in nursing homes, medical practices and hospitals, particularly for the vulnerable elderly group. The resurgence of severe RSV infections in adults in 2022/2023, coinciding with the further withdrawal of protective measures, lends support to this hypothesis. In both age groups, however, only sporadic Influenza infections were observed in 2021/2022.

The period between early November and late December 2022, in particular, presented an exceptional challenge for children’s hospitals, given the very high number of children hospitalized for respiratory tract infections. This surge was caused by the simultaneous occurrence of the strongest RSV and influenza waves since the start of recording in 2016 (Figure a). Especially in children (but to a lesser extent also in adults), a continuous increase in hospitalizations for RSV and Influenza is noted over the entire observation period since 2016 which cannot be explained by changes in testing, inpatient admission practices or catchment area. In other parts of Europe, too, similar observations and assessments have been made (4). Since the number of RSV- and influenza-related hospitalizations had already risen significantly and steadily before the pandemic, it is reasonable to assume that the extreme strain on hospitals in 2022 was not a one-time event, but that situations where the maximum capacity is exceeded will re-occur in the future.

Looking at the seasonality of hospitalization waves for RSV after the pandemic reveals that the waves “migrate” back toward their original time of occurrence as the pandemic wanes. Thus, it can be expected that the wave of hospitalizations for RSV in children will peak between Mid-December 2023 and end of January 2024 and in adults about four weeks later. Hence, a specific preparation for this period would seem advisable. Besides other measures such as vaccination, infection control measures, targeting vulnerable elderly patient groups in particular, could help protect people at risk and prevent inpatient care from becoming overwhelmed, as it has been shown already before and during the COVID-19 pandemic.

Conflict of interest statement
The authors declare that no conflict of interest exists.

Manuscript received on 8 February 2023, revised version accepted on 24 April 2023.

Translated from the original German by by Ralf Thoene, MD.

Cite this as:
Kiefer A, Kabesch M, Ambrosch A: The frequency of hospitalizations for RSV and influenza among children and adults—an analysis from the years 2016–2022. Dtsch Arztebl Int 2023; 120: 534–5. DOI: 10.3238/arztebl.m2023.0111

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