Non-pharmacologic Interventions Not Viable in Stopping Spread of RSV, Flu Over Long Term

Non-pharmacologic interventions similar to those used during the COVID-19 pandemic may limit the spread of endemic diseases, such as respiratory syncytial virus (RSV) and influenza, according to a study published in the Proceedings of the National Academy of Sciences.

Non-pharmaceutical interventions (NPIs) include masking, social distancing, and handwashing. The study authors sought to determinewhether longer-term implementation of these measures could reduce flu and RSV outbreaks over the long term.

The study used epidemic models to evaluate whether a hypothetical longer duration of mask-wearing and other interventions could reduce the spread of endemic infections, such as RSV and the flu.

“Our results show that interventions such as mask-wearing and social distancing are effective at limiting the spread of respiratory disease,” said lead study author Rachel Baker, PhD, in a press release. “However, the strong reductions in cases of endemic diseases, such as RSV and influenza, that we saw during the pandemic may not last if these measures were implemented long-term. It depends on the underlying biology of the disease.”

In these models, case numbers for both diseases were found to decline significantly during the initial introduction of NPIs; however, the modeled epidemics returned over a period of several years regardless of whether the NPIs were still in place.

“We found that for pathogens with a lower intrinsic transmission rate, such as influenza, these return outbreaks were of reduced epidemic peak size, but for pathogens with a higher intrinsic transmission rate, such as RSV, return outbreaks were of a similar size to the pre-NPI period,” Baker said in the release.

The investigators also analyzed the effect of vaccination, which showed that vaccines were able to successfully limit the size of return epidemics.

“These results speak to the power of vaccination as a tool for limiting infectious disease spread,” Baker added.

The investigators said that without vaccination, flu or RSV epidemics could still rise regardless of NPIs being in place. The study authors used various modeled scenarios, which showed that long-term implementation of NPIs increases the susceptibility to infection and increases the effective transmission rate, until the eventual return of the epidemic.

They wrote that over the long term, substantial reductions in incidence are difficult to maintain, specifically in high R0 pathogens, adding that “these effects derive from the dynamics of susceptibility; long-term NPIs may lead to a substantial increase in susceptibility that can lead to a spike in incidence if later relaxed or if a more transmissible strain emerges.”

They added that NPIs are effective on an individual level, but immunization is vital to mitigate the spread of infection as new variants emerge.

“The pandemic shows us that effective masking can offer protection and mitigate transmission at the individual level,” co-senior author Bryan Grenfell, Princeton’s Kathryn Briger and Sarah Fenton professor of Ecology and Evolutionary Biology and Public Affairs at Princeton University, said in a press release. “However, models show that the population consequences of long term NPIs can be more complex, depending on host-pathogen biology.”

Reference

Baker R, Saad-Roy CM, Park SW, Farrar J, Metcalf CJ, Grenfell BT. Long-term benefits of nonpharmaceutical interventions for endemic ... PNAS. https://www.pnas.org/doi/10.1073/pnas.2208895119. Published November 29, 2022. Accessed December 5, 2022.