COVID-19

Scenario Modeling Hub

A Note on Scenario Modeling Hub Round 13 (April 15, 2022)

In a new round of projections, the Scenario Modeling Hub evaluated the trajectory of COVID-19 in the coming year under different assumptions about the durability of the immune response to SARS-CoV-2 and the emergence of a hypothetical new variant in late Spring 2022.

Our main findings include:

  • There is high uncertainty in the future trajectory of the pandemic over the 52-week projection period March 2022-March 2023, although outbreaks are projected to be less intense than in the acute phase of the pandemic. There may be occasional periods of increased incidence, although the timing of these periods varies depending on the model considered and assumptions about immunity and variants.
  • Moderate rises in hospitalizations and deaths are plausible in the next year, relative to March 2022 levels. A shorter duration of immunity against infection (a median of 4 months vs 10 months) and the arrival of an immune escape variant would hasten these rises.
  • Based on a subset of models that include the rise of BA.2 Omicron variant and/or a reduction in social distancing, we anticipate a moderate rise in incidences between April-June 2022.
  • During March 2022- 2023, 95,800 cumulative deaths (95% projection interval [PI] 9,000 to 324,000) are projected to occur in the most optimistic scenario (slow waning of immunity and absence of a new variant). This corresponds to 1.06M cumulative deaths (95% PI 0.98-1.29M) since the start of the pandemic, March 2020-March 2023. In the most pessimistic scenario (fast waning and with emergence of an immune escape variant), 211,000 cumulative deaths would occur during March 2022-2023 (95% PI 52,000-466,000).
  • See our companion statement regarding the date at which we expect to reach 1M deaths

These projections have several caveats and limitations:

  • There is little agreement between models in the timing of future outbreaks.
  • The epidemiological characteristics and timing of emergence of future variants is particularly uncertain. Our analysis is limited to the case of a moderate immune escape variant that arises in May 2022.
  • It is likely that SARS-CoV-2 testing behavior and reporting of cases and deaths will change in the coming year as COVID19 settles into an endemic pattern. These changes are difficult to fully anticipate and model.

COVID-19 Milestone: Reaching 1 Million Deaths in the United States (COVID-19 Scenario Modeling Hub - April 8, 2022)

As part of the thirteenth round of COVID-19 scenario projections, the COVID-19 Scenario Modeling Hub has aggregated projections from 7 modeling teams and generated ensemble estimates for the date at which the United States will cross 1 million cumulative COVID-19 deaths, for multiple scenarios spanning uncertainties about the persistence of immunity to the virus. While we may be seeing the end of the acute phase of the pandemic, we feel it is important to take a moment and reflect on this somber milestone and the lives lost during two years of the pandemic.

The COVID-19 Scenario Modeling Hub estimates that, absent the emergence of a new variant, the United States will most likely cross 1 million deaths in June or early July 2022 (see Figure). However, there is substantial uncertainty as to when we will reach this milestone, with the range of dates this event is likely to occur (i.e., the 50% projection interval) spanning May 5 to November 14 at the time projections were made (March 13, 2022). This range captures both the uncertainty between individual models, uncertainty within models, and uncertainty about exactly how long immunity against COVID-19 persists (as detailed in Scenarios A and C).

The emergence of a new variant or other unforeseen event could accelerate this timeline. While it is impossible to know what the properties and timing of such a variant would be, in this round the COVID-19 Scenario Modeling Hub did consider scenarios where a hypothetical variant with moderate immune escape emerged and started circulating in the United States on May 1, 2022. While the considered hypothetical variant did not substantially impact the earliest or most likely time we might see deaths cross 1 million, it did make a longer wait until this milestone less plausible.

These projections come with the caveat that there also continues to be high variability in the reporting of COVID-19 deaths. There have been notable changes in death reporting in recent months in US states which makes model calibration difficult, and may affect our projections. There have also been substantial backfilling and negating of reported deaths in recent months, so we may be closer (or even past) or further from this milestone than we currently realize. We also should acknowledge that it is likely we have already passed this milestone given that many deaths from COVID-19 may not be identified as such, and 1.1 million excess deaths have been estimated to have already occurred (https://www.economist.com/graphic-detail/coronavirus-excess-deaths-tracker).

Figure. Estimates of the date at which the United States crosses 1 million cumulative deaths nationally, from round 13 of the COVID-19 Scenario Modeling Hub.

Table 1. Ensemble estimates of the date to crossing 1 million reported deaths nationally in the US for four scenarios. Estimates are reported as median and interquartile range (in parentheses).

Table 2. COVID-19 Scenario Modeling Hub round 13 scenarios. More detailed scenario definitions and model characteristics can be found at https://github.com/midas-network/covid19-scenario-modeling-hub.


Rationale

Even the best models of emerging infections struggle to give accurate forecasts at time scales greater than 3-4 weeks due to unpredictable drivers such as a changing policy environment, behavior change, the development of new control measures, and stochastic events. However, policy decisions around the course of emerging infections often require projections in the time frame of months. The goal of long-term projections is to compare outbreak trajectories under different scenarios, as opposed to offering a specific, unconditional estimate of what “will” happen.

As such, long-term projections can guide longer-term decision-making while short-term forecasts are more useful for situational awareness and guiding immediate response. The need for long-term epidemic projections is particularly acute in a severe pandemic, such as COVID-19, that has a large impact on the economy; for instance, economic and budget projections require estimates of outbreak trajectories in the 3-6 month time scale.