December 22, 2021
The impact of respiratory syncytial virus (RSV) will likely be greater in 2021 and 2022 in the United States than in previous years as a result of the ongoing COVID-19 pandemic, based on data from a simulation-modeling study involving approximately 19 million individuals.
Although RSV usually follows consistent patterns of timing and duration, the disease all but disappeared starting in March 2020 after the introduction of measures to mitigate the spread of COVID-19, Zhe Zheng, MBBS, of Yale University, New Haven, Conn., and colleagues wrote.
However, lifting of mitigation measures has resulted in emergence of RSV in various parts of the world in early 2021, and trends may be similar in the United States, but data are needed to plan for prophylaxis and hospital use, they noted.
In a study published in JAMA Network Open, the researchers developed a simulation model for epidemics of RSV based on historical data. They acquired inpatient records from New York during 2005-2014 and from California during 2003-2011. The primary clinical outcome was the estimated monthly hospitalizations for RSV.
The simulated study population was 19.45 million individuals. After evaluating several scenarios including continued low transmission associated with social distancing and other mitigation measures, the researchers focused on the likely scenario that introduction of RSV from other regions would likely spark RSV epidemics in the United States.
They determined that spring and summer 2021 would show an increase in hospitalizations for RSV. Overall, higher rates of virus introduction from other regions were associated with more intense spring and summer RSV epidemics, with the trade-off of smaller winter epidemics. In the model, the expected RSV epidemic in spring and summer 2021 in New York was small, with a peak incidence of 419 hospitalizations per 100,000 people in April; by contrast, for states with less seasonal variability, such as Florida, the model predicted a larger summer epidemic.
In the model, the mean age of hospitalization for children younger than 5 years for January 2022 was expected to be 1.17 years, compared with 0.84 years in January 2019, the researchers noted.
Across all age groups, the greatest relative increase in the incidence of RSV infection was predicted for children aged 1-4 years (ranging from 82% to 86%), as were lower respiratory infections (87%-101%) and hospitalization (99%-119%), compared with prepandemic levels.
Hospitalizations for children aged 1 year were predicted to double compared with prepandemic seasons; 707 per 100,000 children per year for 2021 and 2022 versus 355 per 100,000 children per year in a typical prepandemic season. However, the largest incidence of lower respiratory infections (30,075 per 100,000) was predicted for infants aged 3-5 months, and the largest incidence of hospitalizations (3,116 per 100,000) was predicted for infants younger than 3 months.
"Without virus importation, the risk of RSV infections across all age groups in the winter of 2021 and 2022 would be greater, as more susceptible individuals were spared from infections in the absence of summer epidemics," the researchers noted.
The older mean hospitalization age seen in the model was similar to the reported median patient age in Australia both before the pandemic and during the reemergent RSV epidemic.
"This makes intuitive sense, since many children born in 2020 were spared from RSV infection due to the low virus activity; these children will be older when they get infected for the first time during the reemergent epidemics," the researchers wrote. "Consequently, stakeholders should consider modifying prophylaxis guidelines to include high-risk infants less than 2 years of age for the 2021-2022 season."
The study findings were limited by several factors including the lack of data on level of virus introduction or on the impact of lack of boosting on infants with only transplacentally acquired RSV antibodies, the researchers noted. Other limitations include the use of historical data and the lack of data on values outside those included in the model, as well as the inability to control for other factors that could influence RSV, such as vaccines or long-lasting antibodies.
However, the results suggest that the rate of imported infections is associated with RSV hospitalizations, and the model effectively captured the RSV epidemics in the United States in spring and summer 2021.
Models Can Guide Clinical Preparations
"Health care simulation modeling is a growing field, with very exciting implications," Lenore Jarvis, MD, of George Washington University, Washington, said in an interview. The field has the potential ability to influence health care in a data-driven way, including, but not limited to, staffing and other hospital operations, as well as patient care decision-making. "In short, accurate modeling and predictions can help us to make informed health care decisions that can lead to increased quality of care, potential cost savings, and even to help save lives," she said.
Although the details of transmission modeling were not mentioned in the study, the authors evaluated the performances of several models and scenarios. "Scenario 4, for example, was focused on in particular because it best captured the observed dynamics [for RSV] that emerged during the spring and summer of 2021," Jarvis said.
"Pediatricians can speak to these trends firsthand. A decrease in expected RSV infections and hospitalizations in 2020, followed by an unprecedented and early increase in RSV infections and severity in 2021, and the factors that the authors account for make sense, such as reintroduction of RSV from other regions and low immunity in the population," she said. "It also makes sense that, in these transmission modeling scenarios, the expected mean age of hospitalization because of RSV increased with a temporary (hopefully) increase in RSV hospitalizations in the 2021 season, and potentially the 2022 RSV season."
As for additional research, Jarvis said she would like to see follow-up data on the RSV transmission modeling. "For example, with scenario 4, does this scenario continue to perform well in other time periods, such as the winter? If the modeling continues to be accurate during other periods of evaluation and reevaluation, this modeling could be very useful in helping pediatric clinics and hospitals to prepare for RSV care and hospital capacity management."
The study was supported by grants to various researchers from the National Institute of Allergy and Infectious Diseases/National Institutes of Health, the National Center for Advancing Translational Science at the National Institutes of Health, and NIH Roadmap for Medical Research. Lead author Ms. Zheng had no financial conflicts to disclose. Her study coauthors disclosed relationships with companies including AbbVie, Merck, Pfizer, GlaxoSmithKline, MedImmune, and Janssen. Jarvis had no financial conflicts to disclose and serves on the Pediatric News editorial advisory board.