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, 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.