In the first round of RSV scenario projection, the RSV
Scenario Modeling Hub generated mid-season hospitalization
estimates for the 29-week period Nov 12, 2023 to June 1,
2024. We considered 4 intervention scenarios representing
the impact of new interventions to mitigate the burden of
RSV, and one counterfactual “status quo” scenario where RSV
control mirrors past years. Intervention scenarios assumed
optimistic and pessimistic levels of coverage and effectiveness
of long-acting monoclonal antibodies (nirsevimab) in infants
under 6 mo, combined with optimistic and pessimistic levels
of coverage and effectiveness of vaccination in seniors 60+ yrs.
Coverage was assumed to saturate at 12% (pessimistic) or 36%
(optimistic) among infants, and 14% (pessimistic) or 29%
(optimistic) among seniors, indexed on past coverage of influenza
vaccines by state and age group. Assumptions regarding efficacy
come from randomized control trials for RSV interventions.
Ensemble projections are based on contributions from 10 teams,
using the trimmed linear opinion pool aggregation approach.
All-age and age-specific estimates of RSV hospitalizations are
provided nationally and for 12 states contributing to RSV-NET
surveillance.
Our main findings include:
- 11% (95% CI 6-16%) of seasonal RSV hospitalizations, or
15,500 nationally (95%CI 9,300-21,600), are projected to
be averted in the most optimistic scenario versus no
intervention (scenario A, optimistic intervention coverage
and high effectiveness in both infants and seniors,
compared to status quo scenario).
- With the most pessimistic assumptions, interventions avert
4% (95% CI 2-6%), or 5,800 (95% CI 3,200-8,400) average
hospitalizations (scenario D, pessimistic intervention
coverage and moderate effectiveness in both infants and
seniors, compared to status quo scenario).
- Projected intervention benefits are highest in the targeted
age groups: 21% (95% CI 16-24%) of RSV hospitalizations
would be averted among seniors over 65 yrs and 15% (95% CI
4-24%) among infants under 1 yr, with 56% of total
hospitalizations averted among infants (optimistic scenario).
- These results correspond to 1.24 (95% CI 0.45-2.03) infant
hospitalization averted per 100 doses of monoclonals delivered
in 2023-24) and 0.04 (0.03-0.05) senior hospitalization averted
per 100 vaccine doses (optimistic scenario).
- The peak and cumulative hospitalization burden of the 2023-24
RSV season is likely to remain lower than that of the last
season which had seen a large and unusual post-COVID-19
rebound of RSV, especially in children.
- Cumulative RSV hospitalizations for the period July 1, 2023 -
June 1, 2024 are projected to reach 168,000 (95,500-303,000)
for the most optimistic scenario compared with 183,000
(95%PI 106,000-315,000) for the counterfactual scenario.
- Ensemble projections suggest a prolonged period of RSV
activity between November and March, with a peak most likely
to occur in mid-December 2023. There is heterogeneity in
projected RSV timing between the 12 states considered in this
analysis, with most likely peak dates ranging between Nov 15,
2023 (Georgia, Tennessee) and Jan 15, 2024 (Utah).
- The combined impact of RSV, influenza, and COVID-19 on
hospitalizations is likely to remain below that of last
season (2022-23). Of note in 2022-23, there was concurrent
activity of influenza, COVID-19, and RSV early in the season,
resulting in a particularly high total hospitalization burden.
Activity of these pathogens is projected to be more asynchronous
this year.
- There is variability between states in the projected timing and
intensity of RSV activity this season, due in part to geographic
differences in the seasonality of RSV, impact of COVID-19 NPIs
since 2020, and differences in testing and transmission
intensities.
A few caveats are worth noting:
- Based on recent data on RSV intervention uptake in the US,
our optimistic scenario A seems most closely aligned with
reality.
- There are differences in the post-pandemic rebound of RSV
across age groups, which are not fully understood nor
accounted for by all models. In particular, projections
tend to underestimate disease burden in seniors. These
differences could be in part due to different strengths of
NPIs between young children and adults during the COVID-19
period (e.g., masking propensities), and age-specific
changes in RSV reporting.
- This is the first round of RSV projections, and there is
limited availability of calibration data or past RSV modeling
experience. This is the first time that the RSV-NET
hospitalization dataset has been used for long-term
projections. RSV-NET covers a fraction of 12 states (9% of the
US population overall).
- Most models assume that RSV interventions will not reduce
infection or transmission, so indirect benefits are close to
zero in ensemble estimates.
- Testing practices continue to evolve in the wake of the
COVID-19 pandemic (e.g., increased use of multi-pathogen
testing), which may affect reported hospitalizations in the
RSV-NET system. This will affect comparison with our
projections and with prior year hospitalization data.
For more detailed information, please consult the
RSV Round 1
Scenario Modeling Hub Report
available on the RSV Scenario Modeling Hub Github.
Table 1. RSV Scenario
Modeling Hub round 1 2023-2024 scenarios.
More detailed scenario definitions and
model characteristics can be found at
https://github.com/midas-network/rsv-scenario-modeling-hub.