Increased Testing May Have Played a Role in RSV Surge After COVID-19 Restrictions

The jump in respiratory syncytial virus (RSV) cases after COVID-19-era social distancing and masking eased was partly due to increased testing in outpatient settings as well as changes to the RSV genome, according to a study published online in Nature Communications.

“The resurgence of RSV in Chicago in the summer of 2021 closely followed the return to in-person learning in April and the recension of the indoor mask mandate in June…,” wrote corresponding author Judd F. Hultquist, PhD, of Northwestern University, Chicago, Illinois, and study coauthors. “Reduced pathogen exposure on account of the widespread use of nonpharmaceutical interventions during the COVID-19 pandemic is subsequently theorized to have produced an ‘immunity debt’ with a larger susceptible population resulting in larger surges of infection.”

The study investigated the factors behind the surge in RSV cases in Chicago, Illinois, after COVID-19 restrictions abated. Researchers looked at hospital data on RSV infections from 2009 through 2023.

According to the findings, the number of severe RSV infections after COVID-19 nonpharmaceutical interventions loosened was actually on par with historical averages. Rates of detection for less severe RSV infections, however, increased dramatically with testing changes.

“During the pandemic, we developed new, relatively cheap diagnostic tests where people could test for RSV, flu, and COVID all at once,” said Dr Hultquist. “This resulted in more people getting tested for RSV even if they weren’t severely ill, and we started catching these infections that otherwise would have been missed. We think that some of the increases in cases, especially in our adult populations, is just because we were changing how we were diagnosing the virus, not necessarily because there was more around.”

The study also found that adults hospitalized with RSV-A were at a higher risk of intensive care admission than adults hospitalized with RSV-B. Additionally, researchers noticed that RSV-B showed several new mutations over the course of the COVID-19 pandemic that, they suspect, could affect its ability to spread and be neutralized by antibodies.

The team will continue to investigate the RSV mutations.

“The first thing that we want to do is explore how these mutations are impacting the biology of the virus,” he said. “Does it change how the virus enters a cell? Does it change our body’s ability to fight the virus? But most importantly, does it change the impact of these therapeutics in preventing the virus from spreading? All of these are questions we can now go back to in the lab and begin to explore.”

References

Rios-Guzman E, Simons LM, Dean TJ, et al. Deviations in RSV epidemiological patterns and population structures in the United States following the COVID-19 pandemic. Nat Commun. 2024;15(1):3374. doi:10.1038/s41467-024-47757-9

Dimmer O. Study examines surge in RSV cases after the COVID-19 pandemic. News release. Northwestern University Feinberg School of Medicine; May 29, 2024. Accessed July 3, 2024.