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Respiratory syncytial virus (RSV) causes annual epidemics of acute respiratory illnesses in children, ranging from mild upper respiratory tract infections to severe lower respiratory tract disease including bronchiolitis or pneumonia. Severe RSV disease occurs primarily in infants younger than 6 months during their first fall and winter season of life.

RSV activity in the United States usually begins in the late fall and extends through spring; peak activity typically occurs in early February, although there can be regional variation.1 Following the institution of nonpharmacologic interventions (eg, masking, physical distancing) for the prevention of COVID-19 in March of 2020, the number of RSV infections in the United States decreased rapidly and dramatically.2 Interactions between SARS-CoV-2 and other respiratory viruses also may have altered RSV epidemiology. RSV activity in the United States remained very low through the traditional 2020-2021 fall-winter season but started to increase in the spring of 2021, with variable numbers of cases throughout the different regions of the United States and continuing over the spring, summer and fall.3 This “interseasonal” activity was a marked deviation from the typical RSV seasonal epidemiology and was not generally followed by a second wave of increased RSV circulation in the winter of 2021-2022.3

Because of the change in RSV circulation, in 2021 the AAP strongly supported consideration for use of palivizumab in eligible patients during the interseasonal spread of RSV. This recommendation applied to regions experiencing high rates of RSV circulation in the spring and summer of 2021.4

As of mid-November 2022, RSV activity in the United States is high in all regions, with substantial numbers of hospitalizations and illnesses. The Centers for Disease Control and Prevention (CDC) monitors RSV activity in the United States in collaboration with state and county health departments and commercial and clinical laboratories. These data are available from the National Respiratory and Enteric Virus Surveillance System (NREVSS).3 Recommendations are published for determining the timing of the onset and offset of RSV seasonal activity based on the levels of viral detection and vary depending on whether antigen or molecular testing is used for surveillance.1,5

With the shift in seasonality noted in 2021 and the current surge in RSV cases, the AAP continues to support the use of palivizumab in eligible infants. For regions that began administering palivizumab in the summer and fall of 2022, the current widespread and intense RSV circulation may lead to a period of disease activity lasting more than the typical 6-month duration. If RSV disease activity persists at high levels in a given region through the fall and winter, the AAP supports providing more than 5 consecutive doses of palivizumab to eligible children. Although there is a paucity of data on the provision of more than 5 consecutive doses, there is no evidence of increased frequency or severity of adverse events with later doses in a 5-dose series nor with doses beyond 5 doses in the few published studies.5,6,7,8 Given this information, together with the known efficacy of palivizumab and unpredictable epidemiology of RSV since the summer of 2021, the AAP recommends programmatic consideration of providing more than 5 consecutive doses of palivizumab depending on the duration of the current RSV surge in a given region of the country.

The AAP will continue to monitor the interseasonal trends and update this guidance as needed if the RSV season extends longer than 6 months.6

Additional Information

Interim Guidance Disclaimer: The COVID-19 clinical interim guidance provided here has been updated based on current evidence and information available at the time of publishing. Additional evidence may be available beyond the date of publishing. 

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American Academy of Pediatrics