RSV’s seasonality returning to normal, new data suggest
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Key takeaways:
- RSV showed signs of returning to its pre-pandemic seasonality this past winter.
- Researchers cautioned that off-season epidemics are still possible.
New data suggest that respiratory syncytial virus may be returning to its pre-COVID-19 seasonality — a winter peak — which could help determine when people should be vaccinated against it, researchers said.
Measures to limit the spread of SARS-CoV-2 — including school closures and mask requirements — brought an early end to the RSV season 3 years ago. COVID-19 mitigation measures disrupted the relatively seasonal respiratory illness for three more seasons after that.
In the United States, RSV is estimated to cause up to 80,000 hospitalizations per year among children aged 5 years or younger, and up to 160,000 hospitalizations and 10,000 deaths per year among adults aged 65 years or older, according to the CDC.
Next month, the FDA will decide whether to approve what would be the first two vaccines against RSV — both targeting older adults. It is also reviewing an RSV vaccine for pregnant people.
RSV’s return to normal seasonality could help determine when people should receive a vaccine, the authors of the new report in MMWR said.
The disruption of RSV’s normal circulation “reduced respiratory virus transmission and led to an accumulation of susceptible persons, resulting in large epidemics with atypical seasonality,” Sarah Hamid, PhD, MPH, an Epidemic Intelligence Service officer in the CDC’s Division of Viral Diseases, and colleagues wrote in the study.
Hamid and colleagues analyzed data on RSV seasonality using PCR test results reported to the National Respiratory and Enteric Virus Surveillance System between July 2017 and February 2023, defining RSV epidemics as weeks when the proportion of positive PCR test results for RSV was 3% or higher.
Nationally, from 2017 to 2020, RSV seasons started in October, peaked in December and ended in April, according to the study.
RSV circulation was historically low in the 2020-2021 season, Hamid and colleagues noted. The 2021-2022 season started in May, peaked in June and ended the following January. The 2022-2023 season started in June, peaked in November and ended in January. The peak occurred later than the 2021-2022 season but earlier than pre-pandemic seasons.
“With several RSV prevention products in development, ongoing monitoring of RSV circulation can guide the timing of RSV immunoprophylaxis and of clinical trials and postlicensure effectiveness studies,” Hamid and colleagues wrote. “Although the timing of the 2022-2023 season suggests that seasonal patterns are returning toward those observed in pre-pandemic years, clinicians should be aware that off-season RSV circulation might continue.”
References:
- CDC. RSV Surveillance and research. https://www.cdc.gov/rsv/research/index.html. Accessed April 6, 2023.
- Hamid S, et al. MMWR Morb Mortal Wkly Rep. 2023;doi:10.15585/mmwr/mm7214a1.
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