No vaccination
Pessimistic vaccination
  • 60+ booster with -50% of flu vaccination uptake*
Optimistic vaccination
  • 60+ booster with +15 percentage points of flu vaccination uptake* (capped at 100%)
Theoretical upper boundary vaccination
  • 60+ booster with 100% coverage
Optimistic waning
  • Protection against infection: 6 months median time to transition to 70% of the initial immunity
  • Protection against severe outcomes: no waning
Scenario A Scenario B Scenario C Scenario D
Pessimistic waning
  • Protection against infection: 6 months median time to transition to 40% of the initial immunity
  • Protection against severe outcomes: 6 months median time to transition to 80% of the initial immunity
Scenario E Scenario F Scenario G Scenario H

See also the full scenario details for more detail on the common set of assumptions teams used to create their models.

In Round 5, we asked modellers to start their projections from the 2023-08-01. Data after this date were not included, and as a result, model projections are unlikely to fully account for later information on, for example, the changing variant landscape or behavioural patterns.

Shared assumptions

We asked all modellers to include the following parameters and assumptions, beyond the assumptions of the Scenario Table above:

Assumptions left to modeller judgement

Modellers should use their own judgement and relevant literature if making assumptions about a number of modelling aspects. Note that the resulting between-team differences due to these assumptions are desired, and reflect uncertainty regarding these aspects. They are a main contributor to the uncertainty of the analysis results.

Round 5 submissions

Round 5 has received submissions from six international modelling teams from across the EU/EEA and beyond. Submissions are from a diversity of modelling approaches, adding to the between-team variability of projections. One team submitted projections for 30 EU/EEA countries, one team submitted for 6 countries, and 4 teams for one EU/EEA country.

Table 1. Participating teams by number of modelled countries, scenarios, age-disaggregation

Results and limitations

We first ask, what is the expected 2023/24 winter COVID-19 burden without any further vaccination? And which age groups would be most impacted? We find that without further vaccination, COVID-19 death burden is projected to be around X-X% (80% credible interval) of last year’s death. We focus here on deaths because other outcomes are less comparable across the years. Without further vaccination, elderly (60+) are projected to contribute little to infections (12-17%), but elderly contribute the majority of hospitalisations (92-98%) and deaths (96-99%). This is because the per-capita rate of hospitalisation for elderly is approximately 5 times higher than that of younger individuals, and for death it is roughly 30 times higher.

We then ask, what is the impact of a high autumn COVID-19 booster uptake on expected burden compared to a low uptake? The results show that a high-uptake booster campaign can reduce deaths substantially. Specifically, while a low-uptake autumn booster campaign reduces projected deaths by up to X% (50% upper credible interval bound, the lower being X), this impact increases to up to X% for a high-uptake booster campaign (lower bound being X). The results are similar for prevention of hospitalisations (X% - X% for a high-uptake campaign). The impact of a booster campaign increases when there is fast immune evasion by variants and/or fast immunity waning. The overall impact of a booster campaign on infections is minimal (<4%), so that for the reduction of COVID-19 spread other measures would be required.

There is a substantial variation in the above estimates, which is partly due to the aggregation across different countries, as well as variation between models, and model assumptions. This variations reflects large unknowns with respect to the level and waning of protection from prior infection, vaccination, and hybrid immunity, characteristics of future variants, seasonality and social behaviour of contact mixing and mobility, the under-ascertainment factor. Note that immunocompromised subgroups, other high-risk groups, or specific settings (e.g., hospitals, LTCF) are not addressed with this modelling.


COVID-19 burden 2023/24 relative to last year

COVID-19 burden 2023/24 by age group

Impact of booster uptake on COVID-19 burden 2023/24

Accounting for imbalanced submissions

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Figure 1: Reduction in cumulative COVID-19 death burden through a 2023 autumn booster campaign relative to the no-booster scenario. Vaccine impact estimates are shown for the high-uptake (top) and the low-uptake (bottom) conditions. Those estimates are then further split by fast and slow immunity waning. The light and dark bars show the 80% and 50% quantiles, respectively..

Additional notes