Scenarios

Information about past and present rounds of scenarios is below. For modellers participating in each round, please refer to the Wiki for the most up to date details. For more general information on our approach to setting scenarios, read more in the About section.

Round 5

Scenarios

Round 5 projections begin from 2023-08-01.

Scenarios: Autumn COVID-19 vaccination campaign; Immunity waning (optimistic/pessimistic)

	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

Assumptions

See our Github Wiki for detailed guidance on the assumptions that modellers used in creating scenario projections.

Findings

See the full report for our findings from Round 5.

Round 4

Scenarios

Round 4 projections begin from 2023-03-15.

Scenarios: Immunity waning (optimistic/pessimistic); New variants (no/yes)

	No new variant Projections are initialised in agreement with the SARS-CoV-2 variants that are circulating at the start of the projection period	New variant (sub-lineage) X Introduction: From 1st May 2023, at least of 0.1% of all new infections are due to a new variant X over 16 weeks Characteristics: Variant X has 30% immune escape against infection and 0% immune escape against severe outcomes, and the same intrinsic transmissibility and severity as currently dominating Omicron sub-lineage
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
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 C	Scenario D

Assumptions

See our Github Wiki for detailed guidance on the assumptions that modellers used in creating scenario projections.

Findings

See the full report for our findings from Round 4.

Round 3

Scenarios

Round 3 projections begin from 2022-09-11.

Scenarios: New vaccination (none/annual/biannual); New variants (optimistic/pessimistic)

	No further vaccination Vaccination as planned* No further vaccination	Annual vaccination Vaccination as planned* 2023 onwards: annual vaccination programme in autumn** Uptake higher in 60+ than <60 age groups	Bi-annual vaccination Vaccination as planned* 2023 onwards: bi-annual (2 per year) vaccination in spring and autumn** Uptake higher in 60+ than <60 age groups
Optimistic variant scenario 20% reduction in immunity against infection 0% reduction in immunity against severe outcome One new variant every 9 months First introduction: 1st October 2022	Scenario A	Scenario B	Scenario C
Pessimistic variant scenario 75% reduction in immunity against infection 20% reduction in immunity against severe outcomes One new variant every 9 months First introduction: 1st October 2022	Scenario D	Scenario E	Scenario F

* Vaccination as planned = Primary schedule + 2 booster doses

** Seasonal vaccination campaigns: Autumn = 15 September to 15 December; Spring = 15 March to 15 June

Assumptions

See our Github Wiki for detailed guidance on the assumptions that modellers used in creating scenario projections.

Findings

See the full report for our findings from Round 3.

Round 2

Scenarios

Round 2 projections begin from 2022-07-24.

Scenarios: Autumn second booster campaign among population aged ‘18+’ or ‘60+’; Vaccine effectiveness is ‘optimistic’(effectiveness as of a booster vaccine against Delta) or ‘pessimistic’ (as against BA.4/BA.5/BA.2.75)

	Age 60+ booster campaign 2nd* booster recommended for 60+ Uptake starts 15th September, and reaches 50% coverage by 15th December	Age 18+ booster campaign 2nd* booster recommended for general population, ages 18+ Uptake starts 15th September, and reaches 50% coverage by 15th December
Optimistic vaccine effectiveness Increased booster vaccine effectiveness to that seen against Delta variant	Scenario A	Scenario B
Pessimistic vaccine effectiveness Reduced booster vaccine effectiveness against infection from BA.4/BA.5/BA.2.75 variants	Scenario C	Scenario D

Assumptions

See our Github Wiki for detailed guidance on the assumptions that modellers used in creating scenario projections.

Findings

See the full report for our findings from Round 2.

Round 1

Scenarios

Round 1 projections begin from 2022-05-22.

Scenarios: Stronger or weaker immunity maintained over time (‘Strong/Weak’); 60+ second booster campaign starting in summer or autumn (‘Summer/Autumn’)

	Slow summer booster campaign 2nd booster recommended for 60+ Uptake reaches 50% of 1st booster coverage by 15th December Uptake starts 15th June*	Fast autumn booster campaign 2nd** booster recommended for 60+ Uptake reaches 50% of 1st booster coverage by 15th December Uptake starts 15th September
Optimistic slow immune waning 60% reduction in immunity against infection In 8 months	Scenario A (‘Strong/Summer’)	Scenario B (‘Strong/Autumn’)
Pessimistic fast immune waning 60% reduction in immunity against infection In 3 months	Scenario C (‘Weak/Summer’)	Scenario D (‘Weak/Summer’)

* If a second booster is already offered to 60+ (Greece, Netherlands), vaccination uptake continues as currently

** If a second booster is already offered to 60+ (Greece, Netherlands), a third booster dose is recommended

Assumptions

Booster campaign

We consider scenarios for a second booster vaccination campaign among the population aged 60+ in each country. This vaccination would typically be a fourth dose, following a completed course of two doses plus a first booster dose. We prescribe a relative reduction in vaccination coverage among this group, where by 15th December, uptake of the second booster reaches 50% of coverage achieved by the first booster campaign.

In the scenarios we vary only the timing of the booster campaign:

• Slow summer campaign: uptake starts 15th June

• Fast autumn campaign: uptake starts 15th September

We note that some countries have already started a second booster campaign.

• For nearly all countries, please continue to use the scenarios as they are. The scenarios ask for modellers to include a second booster dose open to ages 60+. In most countries currently offering a second booster, these scenarios are an expansion of the eligible age group

• The exceptions are Greece and the Netherlands, where second booster vaccination is already open to ages 60+. In these two countries:

  • In scenarios A & C (uptake starts in June), please model booster vaccination uptake among the 60+ as it is continuing now.
  • In scenarios B & D (uptake starts in September), please model a third booster (fifth dose), with otherwise the same parameters (uptake among 60+, starting 15 September, coverage reaching 50% of first booster dose by December)

Assumptions about the booster campaign

Shared assumptions

All modellers should include the following parameters when modelling the booster campaign:

• Second booster is only recommended for population aged >=60 years

• Uptake among the target population reaches 50% of coverage achieved by the first booster campaign among that population

• Uptake at 50% of the target population is reached by 15th December

Assumptions left to modeller judgement

Modellers should use their own judgement and relevant literature if making assumptions about the following:

• The existing level of vaccination coverage reached in the first booster campaign

• Vaccine effectiveness against both infection and severe disease, for both previous vaccinations and the second booster

Waning immunity

Waning immunity means protection against new COVID-19 infection. We take a similar general approach to waning immunity as in Round 0 (Euro Scenario Hub) and Round 13 (US Scenario Hub). We specify that immunity wanes to a 60% reduction from baseline levels. The baseline is the level of protection reported immediately after exposure (vaccination or infection).

In the scenarios we vary the median time taken to reach this reduction of immunity:

• Optimistic slow waning: a median time of 8 months for immunity to wane by 60% from baseline

• Pessimistic fast waning: a median time of 3 months for immunity to wane by 60% from baseline

Assumptions about waning immunity

Shared assumptions

All modellers should include the following parameters when modelling waning immunity:

• New to this round

  • Immunity wanes by 60% (i.e. immunity after 3 or 8 months is 40% of baseline) across all scenarios

  • Waning against severe disease: this is now left to modeller judgement with a recommendation to include waning against severe disease - see below

• As the pilot round (text adapted from US Scenario Hub)

  • We prescribe the relative reduction in protection against infection after the waning period, where comparison is to the levels observed immediately after natural infection or vaccination

Assumptions left to modeller judgement

Modellers should use their own judgement and relevant literature if making assumptions about the following:

• Waning of protection against severe disease

  • We strongly recommend including a decrease of 20% protection within 3 months. This is a combined estimate based on various recent studies, see example.
  • However, this is up to modeller judgement and teams should continue to produce results even if they are unable to include waning against severe disease

• The absolute baseline level of protection against infection or severe disease after exposure

• Whether the baseline level of protection varies by the source of immunity (vaccination or natural infection)

• Whether or how new exposure to infection or vaccination during the waning period increases the level of immunity. Teams can choose to bump individuals to a higher level of protection after repeat exposures (where exposure is vaccination or infection), but waning would still occur on a 3 to 8 month timescale after each new exposure

• The distribution of waning immunity, including

  • the shape and rate at which immunity wanes, as long as the median is 3 or 8 months

  • whether immunity reaches a plateau or continues to wane after that time

For additional background on waning immunity, we suggest exploring the scenarios for Round 0 or the more extensive documentation for the US Scenario Hub Round 13.

Additional shared assumptions

We also ask modellers to assume the following:

• No new variant of concern

• No novel vaccine types or novel drugs that strongly impact burden

Findings

See the full report for our findings from Round 1.

Round 0

Scenarios

We ran a pilot round (“Round 0”) over March-May 2022. Round 0 projections begin from 2022-03-13.

Scenarios: Stronger/weaker immunity maintained over time; None/New immune evading variant introduced May 2022

	No new variant Projections are initialized with the mix of strains circulating at the start of the projection period	New variant X Introduction: From May 1st 2022 is a continuous influx of 50 weekly infections of variant X over 16 weeks Characteristics: Variant X has 30% immune escape, and the same intrinsic transmissibility and severity as Omicron.
Optimistic waning of protection Speed: 10 months median time to transition to partial immunity Plateau: 40% reduction in protection from baseline (protection immediately after exposure) at plateau	Scenario A	Scenario B
Pessimistic waning of protection Speed: 4 months median time to transition to partial immunity Plateau: 60% reduction in protection from baseline level at immune plateau	Scenario C	Scenario D

Assumptions

The details for this round identically match those of the US Scenario Hub, applied to the 32 countries of the European Hub.

• Round 0 overview
• Full scenario details - US Hub

Findings

In Round 0:

• 20 independent teams joined calls and/or submitted models

• 8 teams started working on Round 0; 5 teams contributed results

• 5 countries had >2 model projections

As it was a pilot round, we provide only general, broad conclusions for Round 0.

• Scientific interpretation
  • Results were consistent with the speed of waning protection against infection as a more significant factor in future outbreaks, compared to a new variant with some immune escape
  • This matched with similar results from the US Hub Round 13
• Policy relevance
  • This indicates greater consideration for the timing of vaccination programmes relative to waning protection, rather than as a response to new variant introductions
• Interpret with caution:
  • Models were intended as experimental for the pilot round, and we found substantial variation between models as well as between countries and scenarios
  • Results may be biased by both submission constraints and scenario confounding

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The European Scenario and Forecast Hubs are run in collaboration between the Epiforecasts team at the London School of Hygiene & Tropical Medicine; and the European Centre for Disease Control and Prevention (ECDC).

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