RSV’s Impact on Vulnerable Populations

Respiratory syncytial virus (RSV) poses a meaningful threat to older adults and individuals with chronic conditions, according to the Centers for Disease control (CDC). Those with asthma, chronic obstructive pulmonary disease, congestive heart failure, and advanced age are especially susceptible to severe illness. The CDC estimates that each year, RSV leads to 100,000 to 150,000 hospitalizations among adults aged 60 and older in the US.

Meta-Analysis of Human Challenge Studies

Human challenge studies (HICs) involve intentionally exposing participants to a pathogen to assess the efficacy of potential treatments or vaccines. While numerous HICs have investigated experimental drugs for RSV, further research is warranted. A recent systematic review and meta-analysis explored the integration of RSV HICs to better understand the virus’s behavior over time.

“These results can be used to contextualize effects of other potential experimental drugs when tested on the same strain.”

Researchers analyzed data from double-blind, placebo-controlled RSV HICs conducted between 1990 and August 2023. They focused on viral load (VL) and symptom-related measures in placebo groups,and also the relative meen reduction (RMR) of these measures in groups receiving experimental drugs. Key outcomes included RMR of VL area under the curve (AUC) and total symptom score (TSS) AUC. The study also examined mean placebo VL and AUC, mean placebo VL at peak, time to mean placebo peak VL, mean placebo TSS AUC, and time to mean placebo peak TSS. A random-effects meta-analysis was used for all outcomes except the time to mean peak VL and TSS.

The analysis revealed that the average time to peak VL for RSV is similar to that of SARS-CoV-2 but occurs later than in influenza infections. The primary outcomes showed an average 54% reduction in VL AUC, with considerable variability across studies. The TSS AUC, though, demonstrated a larger average reduction of 76% and lower heterogeneity, suggesting more consistent treatment effects.

In terms of symptom progression, peak TSS occurs later in SARS-CoV-2 infections and earlier in influenza. For RSV, peak VL and TSS coincide, whereas in SARS-CoV-2 and influenza, peak TSS is delayed by 2 and 1 days, respectively.

The study authors noted that RSV challenge studies typically randomize individuals between day 2 and day 5 post-inoculation, assuming all are RSV positive. However, a small proportion may test positive after randomization, which may not fully reflect clinical treatment. Despite optimized screening, the uninfected rate varied across studies, potentially introducing heterogeneity due to factors like prior RSV exposure, innate or cell-based immunity, and variable RSV-specific immunity in volunteers. Other potential sources of heterogeneity include imbalances in VL and symptom severity,prior infection timing,seasonal differences,varying drug mechanisms,and unmeasured confounders.

the findings indicated an average 54% reduction in VL AUC with high heterogeneity, while the TSS AUC showed a more consistent 76% reduction.