RSV seasonality returns to normal, new data shows

Key points to remember:

• RSV showed signs of returning to its pre-pandemic seasonality last winter.
• Researchers have warned that out-of-season outbreaks are still possible.

New data suggests 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 have said.

Measures to limit the spread of SARS-CoV-2 – including school closures and mask requirements – ended the RSV season prematurely 3 years ago. COVID-19 mitigation measures disrupted the relatively seasonal respiratory disease for three more seasons thereafter.

In the United States, RSV is estimated to cause up to 80,000 hospitalizations per year in children age 5 or younger, and up to 160,000 hospitalizations and 10,000 deaths per year in adults age 65 or older. more, according to the CDC.

Next month, the FDA will decide whether to approve the first two RSV vaccines — both targeting the elderly. It also reviews an RSV vaccine for pregnant women.

RSV’s return to normal seasonality could help determine when people should get a vaccine, according to the authors of the new report in MMWR said.

Disruption of normal RSV circulation “has reduced respiratory virus transmission and led to an accumulation of susceptible individuals, resulting in large outbreaks with atypical seasonality.” Sarah Hamid, PhD, MPH, an Epidemic Intelligence Officer from the CDC’s Viral Diseases Division and his 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 outbreaks as weeks when the proportion of positive PCR test results for RSV was 3% or more.

Nationally, from 2017 to 2020, RSV seasons began 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 2021-22 season started in May, peaked in June and ended the following January. The 2022-23 season started in June, peaked in November and ended in January. The peak occurred later than the 2021-2022 season but earlier than the pre-pandemic seasons.

“With several RSV prevention products in development, continuous monitoring of RSV circulation may guide the timing of RSV immunoprophylaxis and post-licensure clinical trials and efficacy studies,” wrote Hamid and colleagues. “Although the timing of the 2022-2023 season suggests seasonal patterns are reverting to those seen in pre-pandemic years, clinicians should be aware that off-season RSV circulation may continue.”

The references: