New Data on RSV Epidemiology from ECCMID 2022

Reducing the morbidity and mortality of respiratory syncytial virus (RSV) disease continues to be an unmet need worldwide. At the 2022 European Congress of Clinical Microbiology and Infectious Diseases (ECCMID 2022), several new reports shed light on the disease burden in older adults, as well as the impact of the COVID-19 pandemic on seasonal trends in RSV.

Longer Hospital Stays With RSV vs Flu
It has been reported consistently that RSV disease burden in older adults is substantial. According to a new retrospective analysis of hospitalized adults in Spain (Torres and colleagues), the RSV-associated hospitalization rate and mortality rate increased with age.

This research was based on the IASSIST clinical database, which captured 75% of the hospital population in Spain. By age group, the hospitalization rates were 1.1, 5.1, 10.8, 26.7, and 55.9 per 100,000 person-years in adults aged 18-50 years, 51-64 years, 65-74 years, 75-84 years, and 85 years or older, respectively (95% CIs not reported). When stratified by the same age groups, the RSV-associated mortality rates were 4.1, 4.8, 5.0, 7.5, and 8.2 per 100,000 person-years.

The data suggest that age is an important risk factor for RSV-associated hospitalization and mortality, although additional large sample size studies with age-specific data are needed to provide more robust evidence.

The authors also compared hospitalization rates and duration of hospitalization for adults with RSV or influenza. They found that, although influenza-associated hospitalization occurred more frequently than RSV in each age group, the average length of hospital stay was longer in patients with RSV.

Interpreting these epidemiologic findings and comparing them with other relevant studies should be done with caution, as several factors may affect the estimates, such as differences in study design (eg, location, population, enrollment criteria, case definition, sample size), RSV seasonality, clinical specimen, diagnostic test, and healthcare-seeking behavior in the underlying population. Moreover, future studies should consider comorbidities when evaluating the role of age in RSV infection, as most older adults have underlying medical conditions.

RSV Seasonality and the COVID-19 Pandemic
The COVID-19 pandemic has introduced changes in the seasonal activity of RSV, partially through the introduction of nonpharmaceutical interventions. At ECCMID 2022, 2 new reports described out-of-season RSV epidemics during the COVID-19 pandemic.

A 6-year study from Spain (Sanchez and colleagues) showed that the RSV epidemic peak occurred every winter except the winter of 2020/2021; instead, RSV appeared starting in June 2021.

Similarly, a 2-year study from Portugal (Melo and colleagues) showed a decrease of RSV activity during the winter of 2020/2021, followed by an increase of RSV circulation during summer starting in July 2021.

Elucidating the factors involved in RSV transmission dynamics will facilitate further understanding of the mechanism behind RSV seasonality, which is important to help countries prepare for RSV rebound in the public health system. Continued RSV surveillance is also critical to assess the impact of COVID-19 on the number of RSV cases, hospitalizations, and deaths.

Summary
RSV infection is an important disease among older adults, highlighting the need for RSV prophylaxis in this age group. Improved surveillance systems applying standard case definitions and reporting practices with a better understanding of morbidity, mortality, and seasonality could help guide targeted interventions, such as vaccination. Multiple RSV vaccines are being researched for use in older adults, and we hope to see updates on their status at future conferences.

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