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Estimating Respiratory Syncytial Virus Resurgence After the COVID-19 Pandemic

Respiratory syncytial virus (RSV) cases decreased due to COVID-19 precautions. Investigators estimated the rate and timing of RSV resurgence over the next few years.

A study published in JAMA Network Open identified the effects of mitigation strategies, duration of maternal-derived immunity, and importation of external factors on RSV epidemic severity.

Using the decreased RSV cases during the 2020 COVID-19 pandemic as a referent, the investigators estimated the number of RSV hospitalizations in each month of the 2021-2025 RSV seasons.

RSV outbreaks in the US have spatiotemporal patterns, or “seasons,” of predictable time and duration. The investigators emphasized the need to model the intensity, timing, and affected ages of RSV epidemics to prepare medical infrastructure for the upcoming years.

The investigators used simulation models to explore factors associated with RSV epidemics. They collected RSV hospitalization data from New York (2005-2014) and California (2003-2011) using the Agency for Healthcare Research and Quality’s State Inpatient Databases of the Healthcare Cost and Utilization Project. The data included age of patient and month of hospitalization. Additionally, the investigators obtained population size information about each age group from the US Census Bureau’s American Community Survey.

The primary clinical outcome monitored was the estimated monthly number of RSV hospitalizations. Secondary outcomes of interest were the age distributions of hospitalized children under 5, incidence of any RSV infection, and incidence of lower respiratory RSV infection. Hospitalization due to RSV was defined as hospitalization for bronchiolitis or pneumonia due to RSV.

The investigators calculated percentage change in RSV incidence by contrasting estimated incidence in the 2021-2022 RSV season. They estimated monthly RSV incidence from 2021-2025 with and without changes to the transmission rate in relation to mitigation measures and virus introduction from external sources.

The study included a hypothetical population of 19.45 million people in the US. The results showed the typical seasonal RSV epidemics were mitigated by COVID-19 measures from 2020-2021. Over the 2021-2022 season, RSV hospitalizations in children 1-4 years old were expected to be double that of a typical RSV season.

This research built upon existing studies by including ages and evaluating the effects of external infection. The investigators noted that the results predicted a return to annual seasonal cycles after the winter of 2021-2022, assuming no external source of infections. They recommended prophylaxis guidelines should be modified to include high-risk infants under 2 years for the 2021-2022 RSV season.