What is the rationale for this outlook for each disease?
Infectious disease experts and scenario models provide evidence that this season is likely to bring a moderate COVID-19 wave, causing around as many hospitalizations at the peak as occurred at last winter’s peak.
There is widespread, population-level protective immunity to COVID-19 from prior infections and/or vaccinations, making it unlikely that COVID-19 will cause very large waves of severe disease or hospitalization, according to modeling by the COVID-19 Scenario Modeling Hub.
COVID-19 could peak earlier than last season, however, because of limited summer activity compared to past years.
Experts anticipate that the influenza season will fall in the typical range of severity. However, even typical seasons vary widely in the number of illnesses, hospitalizations, and deaths.
Experts do not believe that the COVID-19 pandemic—and associated interventions and behavior changes—will continue to have a major impact on influenza transmission, following reduced influenza activity in 2020-2021 and an early peak for the 2022-2023 season.
Experts anticipate that RSV is likely to return to normal season patterns following a severe season last year.
Last year’s season likely elevated population immunity to typical levels, which had previously been lower because of reduced RSV circulation early in the COVID-19 pandemic.
There are also new RSV prevention tools available, which could potentially decrease hospital burden. These include vaccines for those aged 60 years and older and an immunization for infants.
What are the key uncertainties?
High immunization uptake could reduce the number of hospitalizations substantially. It is difficult to predict the size and timing of peak activity for each disease, as well as how the timing might overlap. These factors will affect the level of strain on the healthcare system. There is also considerable uncertainty about the level of vaccine uptake, particularly for the RSV vaccine for older adults and RSV immunization for infants that are new this season.
The COVID-19 pandemic changed patterns for influenza and RSV circulation, and there could be lingering effects on population immunity or behavior that continue to affect influenza or RSV levels this season. Other disease-specific uncertainties include the following:
The virus that causes COVID-19 is constantly changing, and a new variant could emerge which is less effectively mitigated by immunity from past infections or from existing vaccines and treatments. COVID-19 has not yet occurred as a regular seasonal disease, so we do not yet fully understand how the timing and magnitude of waves will vary.
We do not yet know which influenza viruses will predominate, which can affect the number of severe illnesses and hospitalizations. We also do not yet know how effective vaccines will be against the predominant viruses.
Particularly for RSV, we have less precise estimates for the burden of illnesses and hospitalizations data on past seasons to inform expectations for this fall/winter.
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