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Estimation of the Timing and Intensity of Reemergence of Respiratory Syncytial Virus Following the COVID-19 Pandemic in the US

Educational Objective
To identify the key insights or developments described in this article
1 Credit CME
Key Points

Question  What are the factors associated with the timing and intensity of reemergent respiratory syncytial virus (RSV) epidemics following the COVID-19 pandemic?

Findings  In this simulation modeling study of a simulated population of 19.45 million people, virus introduction from external sources was associated with the spring and summer epidemics in 2021. Reemergent RSV epidemics in 2021 and 2022 were projected to be more intense and to affect patients in a broader age range than in typical RSV seasons.

Meaning  These findings suggest that the timing and intensity of reemergent RSV epidemics might be different from the usual RSV season, depending on the duration of mitigation measures and the extent of virus introduction from other regions.


Importance  Respiratory syncytial virus (RSV) is a leading cause of hospitalizations in young children. RSV largely disappeared in 2020 owing to precautions taken because of the COVID-19 pandemic. Estimating the timing and intensity of the reemergence of RSV and the age groups affected is crucial for planning for the administration of prophylactic antibodies and anticipating hospital capacity.

Objective  To examine the association of different factors, including mitigation strategies, duration of maternal-derived immunity, and importation of external infections, with the dynamics of reemergent RSV epidemics.

Design, Setting, and Participants  This simulation modeling study used mathematical models to reproduce the annual epidemics of RSV before the COVID-19 pandemic in New York and California. These models were modified to project the trajectory of RSV epidemics from 2020 to 2025 under different scenarios with varying stringency of mitigation measures for SARS-CoV-2. Simulations also evaluated factors likely to affect the reemergence of RSV epidemics, including introduction of the virus from out-of-state sources and decreased transplacentally acquired immunity in infants. Models using parameters fitted to similar inpatient data sets from Colorado and Florida were used to illustrate these associations in populations with biennial RSV epidemics and year-round RSV circulation, respectively. Statistical analysis was performed from February to October 2021.

Main Outcomes and Measures  The primary outcome of this study was defined as the estimated number of RSV hospitalizations each month in the entire population. Secondary outcomes included the age distribution of hospitalizations among children less than 5 years of age, incidence of any RSV infection, and incidence of RSV lower respiratory tract infection.

Results  Among a simulated population of 19.45 million people, virus introduction from external sources was associated with the emergence of the spring and summer epidemic in 2021. There was a tradeoff between the intensity of the spring and summer epidemic in 2021 and the intensity of the epidemic in the subsequent winter. Among children 1 year of age, the estimated incidence of RSV hospitalizations was 707 per 100 000 children per year in the 2021 and 2022 RSV season, compared with 355 per 100 000 children per year in a typical RSV season.

Conclusions and Relevance  This simulation modeling study found that virus introduction from external sources was associated with the spring and summer epidemics in 2021. These findings suggest that pediatric departments should be alert to large RSV outbreaks in the coming seasons, the intensity of which could depend on the size of the spring and summer epidemic in that location. Enhanced surveillance is recommended for both prophylaxis administration and hospital capacity management.

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Article Information

Accepted for Publication: November 8, 2021.

Published: December 16, 2021. doi:10.1001/jamanetworkopen.2021.41779

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Zheng Z et al. JAMA Network Open.

Corresponding Author: Zhe Zheng, MPhil, MBBS, Department of Epidemiology of Microbial Diseases, Yale University, 60 College St, New Haven, CT 06511 (

Author Contributions: Miss Zheng had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Pitzer, Shapiro, Bont, Weinberger.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Zheng, Bont, Weinberger.

Critical revision of the manuscript for important intellectual content: Pitzer, Shapiro, Bont, Weinberger.

Statistical analysis: Zheng, Pitzer, Bont.

Obtained funding: Pitzer, Weinberger.

Administrative, technical, or material support: Zheng, Shapiro, Bont.

Supervision: Pitzer, Shapiro, Weinberger.

Conflict of Interest Disclosures: Dr Pitzer reported receiving reimbursement from Merck and Pfizer for travel expenses to Scientific Input Engagements on respiratory syncytial virus. Dr Weinberger reported receiving consulting fees from Pfizer, Merck, GlaxoSmithKline, and Affinivax and is principal investigator on research grants from Pfizer and Merck outside the submitted work. Dr Bont reported receiving grants from AbbVie, MedImmune, Janssen, Pfizer, MeMed, and the Bill & Melinda Gates Foundation. No other disclosures were reported.

Funding/Support: Drs Weinberger and Pitzer received support from grants R01AI137093 from the National Institute of Allergy and Infectious Diseases/National Institutes of Health. Dr Shapiro was supported, in part, by grants number UL1TR000142 and KL2-TR001862 from the National Center for Advancing Translational Science (NCATS) at the National Institutes of Health (NIH) and NIH Roadmap for Medical Research.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Disclaimer: The contents of this manuscript are solely the responsibility of the authors and do not necessarily represent the official views of NIH.

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