Jyoti Kinghorn 
Respiratory syncytial virus (RSV) is a seasonal virus like the influenza virus, often circulating in the colder fall and winter months. But while the flu virus mutates constantly, the RSV virus may be a lot slower to mutate. The recent surge in RSV-related hospitalization was analyzed by scientists and the strains of RSV causing this surge were identified.
A surge in RSV hospitalization in recent years
In most adults, RSV causes symptoms resembling those of the common cold. However, in children under the age of 5 and seniors over the age of 60, RSV can cause serious complications such as pneumonia that can require hospitalization.
In recent years as the world emerged from the COVID-19 pandemic, we saw a surge in hospitalizations because of complications after RSV infection. This has been attributed to the reduced population-level immunity to the virus due to less frequent encounters with it during the pandemic years.
Widespread acceptance and administration of the RSV vaccines which were FDA-approved in 2023 may bring the number of hospitalizations from RSV down and provide relief on a population level.
But how often do we need RSV vaccines or boosters? Does RSV mutate like the influenza viruses which require an updated vaccine each year? Recent genomic surveys indicate that RSV does not mutate like the flu virus.
Research from Boston
Researchers from Massachusetts General Hospital and the Broad Institute of MIT and Harvard studied RSV viral lineages during the surge of RSV infections in 2022.
They used genome sequencing to sequence 105 samples of patients diagnosed with RSV infection who visited the Massachusetts General Hospital or its outpatient practices. Genome sequencing gives scientists information about the composition of the virus’s genome, leading to the identification of strains or mutations. The authors believed their samples to be representative of the overall United States.
From the 77 usable gene sequences, they detected multiple strains of RSV-A (70 samples) and RSV-B (7 samples). Tracing back the sequences, the most recent common ancestor of the RSV-A strains was estimated to have existed between 2014-2017, and for RSV-B strains it was estimated to have been in 2019. No new virulent strains were identified.
This work shows that while the RSV virus also evolves, it is much slower than the flu virus.
Research from Washington State
In their article published in the CDC’s Emerging Infectious Diseases journal, researchers from the University of Washington and the Fred Hutchinson Cancer Research Center studied the genomes of RSV virus strains in King County, Washington for two seasons- 2021-2022, and 2022-2023.
Dr. Stephanie Goya and colleagues extracted RNA from excess samples obtained from individuals who sought care at the University of Washington during these seasons, and whose samples were checked positive for RSV by PCR. A majority of these patients were outpatients.
Among 54 samples, they found 31 samples to have the RSV-A subtype (1 from 2021-22, and 30 from 2022-23) and 23 samples to have the RSV-B subtype (13 from 2021-22, and 10 from 2022-23). In these subtypes, the researchers identified strains that have been circulating in the U.S. over the last 10 years, suggesting that the virus does not mutate often.
In their article, the researchers say, “Detected RSV strains have been spreading for >10 years, suggesting a role for diminished population immunity from low RSV exposure during the COVID-19 pandemic”.
They also caution that continued efforts to sequence RSV strains are necessary to keep track of possible future mutations, saying, “With likely future widespread availability of RSV vaccines, continued real-time RSV genomic surveillance will be required to monitor the evolution and emergence of new viral strains”.
The information provided in our blog posts is for informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this blog.
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