Public health impact of UK COVID-19 booster vaccination programs during Omicron predominance

Figures & data

Figure 1. Dynamic transmission model structure.

Compartments – all compartments were further stratified by age: S – susceptible; V_{1,2,B, BW –} vaccinated with dose 1, dose 2, boosted, and boosted with protection against infection having waned; E, EV_1,2,B – exposed by vaccination status; I_{S, V1S, V2S, VBS} – infectious and symptomatic by vaccination status; I_{A, V1A, V2A, VBA} – infectious and asymptomatic by vaccination status; R – recovered; Parameters: υ_{1, 2, B} – coverage by vaccination status; λ – force of infection; σ_{1, 2, B} – vaccine effectiveness against infection by vaccination status; ψ_{0,1, 2, B, BW} – waning rate (1/duration of immunity) by infection-induced immunity and vaccination status; ε_{1, 2, B} – probability of displaying symptoms by vaccination status; γ – recovery rate (1/duration of symptoms); Κ – rate of progression to infectious disease

Table 1. Vaccine- and infection-induced protection inputs.

	PV dose 1	PV dose 2	Booster	Prior Infection
Effectiveness (%)
Infection	50.5 [41] ^a	74.5 [41] ^a	55.0 [43] ^b	100 ^c
Reduction in probability of symptoms ^d	5.9 [41]	19.1 [41]	12.0 [42]	-
Hospitalization	86.6 [40] ^e	97.0 [37] ^f	90.0 [43] ^b	-
Mortality	88.5 [40] ^e	97.0 [37] ^f	90.0 [43] ^b	-
Duration of protection (months)
Infection	6.00 ^g	6.00 ^g	5.43 ^h	2.04 ^i
Reduction in probability of symptoms ^d	6.00 ^g	6.00 ^g	9.72 ^h	-
Hospitalization	6.00 ^g	6.00 ^g	9.72 ^h	-
Mortality	6.00 ^g	6.00 ^g	9.72 ^h	-
Rate of waning (per week)
Infection	0.042 ^j	0.042 ^j	0.043 ^k	0.114 ^j
Reduction in probability of symptoms ^d	0.042 ^j	0.042 ^j	0.024 ^l	-
Hospitalization	0.042 ^j	0.042 ^j	0.024 ^l	-
Mortality	0.042 ^j	0.042 ^j	0.024 ^l	-

Abbreviations: DoP, duration of protection; PV, primary series vaccination; VE, vaccine effectiveness

^aBrand-agnostic VE calculated from Pouwels et al. (pre-print) [41] UK-specific data for vaccine-specific effectiveness estimates during a Delta-dominant period, and weighted by vaccine uptake

^bUK Vaccine Effectiveness Expert Panel consensus estimates of booster VE within 0–3 months based on the use of BNT162b2 or mRNA-1273 booster and assuming primary series vaccination with BNT162b2, as reported in UK COVID-19 weekly vaccine surveillance report from 24 March 2022 [43]

^cAssumed protection against re-infection after Omicron infection

^dBased on proportion of patients reporting any symptoms 1–20 days after PV dose 1 or ≥14 days after PV dose 2 compared to those not vaccinated. Assumed to be the same for all vaccines

^eBrand-agnostic VE for PV dose 1 calculated from Andrews et al. (pre-print) [40] UK-specific data for vaccine-specific effectiveness estimates for all age groups during a Delta-dominant period, at least 4 weeks after PV dose 1, and weighted by vaccine uptake of 50% BNT162b2 and 50% ChAdOx1

^fCalculated as the midpoint of UK Vaccine Effectiveness Expert Panel consensus estimates of VE against the Delta variant for PV dose 2, within 0–3 months of vaccination, as reported in the UK COVID-19 weekly vaccine surveillance report from 20 January 2022. Estimates are brand-agnostic and are characterized as ‘high-confidence’ estimates (Hospitalization: 95–99%; Mortality: 95–99%)

^gAssumed

^hDuration of protection calculated as 1/waning rate

ⁱThe DoP against re-infection after Omicron infection was calculated by multiplying the assumed DoP of infection-induced immunity after Delta infection (assumed to be 9 months) by the relative strength of protection against infection from Delta (84% based on [65]) versus Omicron (19% based on [66]). This DoP begins after the patient leaves the ‘infectious’ compartment

^jRate of waning protection calculated as 1/duration of protection

^kWaning rate calculated as the rate of loss of protection against symptomatic disease based on the use of BNT162b2 or mRNA-1273 boosters from the UK COVID-19 weekly vaccine surveillance report from 31 March 2022 [36]

^lWaning rate calculated as the rate of loss of protection against hospitalization based on the use of BNT162b2 or mRNA-1273 boosters, from the UK COVID-19 weekly vaccine surveillance report from 31 March 2022 [36]

Table 2. Health and NHS resource use inputs.

	Age group (years)
	<0.5	0.5–4	5–11	12–15	16–17	18–29	30–49	50–64	65–74	≥ 75	All ages	Source
Health
Probability of symptoms (%)	40	40	25	37	42	51	59	72	76	76	-	Derived from [56]
Proportion hospitalized ^a (%)	1.7	1.7	0.4	0.4	0.9	1.0	1.9	5.7	17.3	45.7	-	^b
Proportion of hospitalized in ICU (%)	0.00	0.00	0.00	0.00	0.00	10.20	26.36	30.41	20.49	6.15	-	^c
Infection fatality ratio ^a,d (%)	0.00	0.00	0.00	0.00	0.00	0.00	0.01	0.39	2.99	20.51	-	Calculated from [52]
High risk
Proportion high risk (%)	5.2	5.2	8.9	9.5	11.2	16.9	26.3	40.5	58.4	76.2	^−	^e
Risk ratio of hospitalization ^f	-	-	-	-	-	-	-	-	-	-	1.70	[53]
Risk ratio of ICU admission ^f	-	-	-	-	-	-	-	-	-	-	1.12	Cited in [54]
Risk ratio of mortality ^f	-	-	-	-	-	-	-	-	-	-	2.15	Cited HR in [54]
Proportion with long COVID (%)
Patients receiving outpatient care ^f	-	-	-	-	-	-	-	-	-	-	32	[67]
Hospitalized patients ^f	-	-	-	-	-	-	-	-	-	-	51	[67]
NHS resource use
Proportion visiting GP ^f,g (%)	-	-	-	-	-	-	-	-	-	-	100	Assumed
Bed days general ward ^f (days/case)	-	-	-	-	-	-	-	-	-	-	8.5	Calculated from [68]
Bed days ICU ^f (days/case)	-	-	-	-	-	-	-	-	-	-	10.06	[63]

Abbreviations: GP, general practitioner; HR, hazard ratio; ICNARC, Intensive Care National Audit & Resource Center; ICU, intensive care unit; NHS, National Health Service; UKHSA, UK Health Security Agency

^aOf symptomatic cases only

^bThe case to hospitalizations ratio was calculated using observed age-stratified UKHSA case and hospitalization data from weeks 45–53, 2020 [55], a period before vaccines against SARS-CoV-2 were widely available. Further details are provided in the Supplementary methods for model calibration

^cDerived from 2021 ICNARC report data on the overall probability of being admitted to an ICU and the age distribution of cases in ICU [63], considering the age distribution of hospitalized cases from UKHSA data

^dIFR inputs were adjusted from the IFRs reported by Nyberg et al. [52] to remove the effects of vaccination and high-risk mortality that were applied in the model simulation itself, to exclude asymptomatic cases, and to match the overall observed IFR in the model calibration period (3 January–3 April 2022). Further details are provided in the Supplementary methods for model inputs

^ePopulation-size weighted average of point prevalence for each age group based on data in Walker et al., 2021 [76]

^fAssumed to be the same across all age groups

^gOf non-hospitalized symptomatic cases only

Figure 2. Base case health outcomes: new cases, hospitalizations, and deaths by week.

Base case new health outcomes (i.e. incidence) by week per 100,000 population with (green) and without (black) the Autumn–Winter_2021–2022 booster vaccination program. A. New cases per week per 100,000 population. B. New hospitalizations per week per 100,000 population. C. New deaths per week per 100,000 population.

Table 3. Base case results: Modeled population-level outcomes between January and April 2022 with the Autumn–Winter 2021–2022 booster program.

Outcomes ^a	No booster	Booster	Outcomes averted with booster ^b
			Number of outcomes averted	% reduction
Health outcomes (n)
COVID-19 cases	19,893,662	7,093,296	12,800,366	64%
Asymptomatic	10,049,496	3,990,662	6,058,834	60%
Symptomatic	9,844,166	3,102,634	6,741,532	68%
Hospitalizations	1,200,143	111,349	1,088,795	91%
General ward cases	1,009,413	91,668	917,745	91%
ICU cases	190,731	19,680	171,050	90%
Long COVID cases	5,491,621	1,759,386	3,732,235	68%
Deaths	310,854	21,258	289,596	93%
NHS resource use outcomes
GP visits (n)	8,644,023	2,991,286	5,652,737	65%
Bed days in general ward	8,580,008	779,179	7,800,829	91%
Bed days in ICU	1,621,211	167,283	1,453,928	90%
Patient productivity loss
Days of work lost	554,648,660	193,289,694	361,358,966	65%

Abbreviations: COVID-19, coronavirus disease 2019; GP, general practitioner; ICU, intensive care unit

^aNew outcomes (i.e. incidence) estimated for the period between 3 January 2022 and 3 April 2022

^bDifference and percent reduction with booster relative to no booster

Figure 3. Scenario projections: Weekly hospitalizations averted with Spring&Autumn_2021–2022 boosters.

Modeled projections of new hospitalizations averted with Spring&Autumn₂₀₂₂ booster vaccination in scenario analyses. New hospitalizations averted are depicted weekly over the extended time horizon of 4 April 2022 to 2 April 2023 for each of the modeled scenarios. Scenario 1: Actual (Spring 2022) and anticipated (Autumn 2022) booster programs. Scenario 2: Alternative Spring&Autumn₂₀₂₂ booster programs extending eligibility to individuals aged ≥5 years. Scenario 3: Alternative Spring&Autumn₂₀₂₂ booster programs extending eligibility to individuals aged ≥5 years and assuming increased uptake among all age groups. Scenario 4: Alternative Spring&Autumn₂₀₂₂ booster programs in which only individuals in Green Book [64] clinical risk groups would be eligible. Scenario 5: Alternative Spring&Autumn₂₀₂₂ booster programs in which only individuals in Green Book [64] clinical risk groups would be eligible and assuming increased uptake in these groups.

Table 4. Scenario results: Modeled percent reduction in population-level outcomes averted between April 2022 and April 2023 with alternative Spring & Autumn 2022 booster program scenarios.

Outcomes ^a	Scenario 1 ^b	Scenario 2 ^c	Scenario 3 ^d	Scenario 4 ^e	Scenario 5 ^f
Health outcomes
COVID-19 cases	13%	64%	75%	27%	33%
Asymptomatic	12%	63%	74%	25%	31%
Symptomatic	15%	66%	76%	29%	34%
Hospitalizations	36%	78%	85%	48%	55%
General ward cases	37%	78%	85%	48%	55%
ICU cases	30%	78%	84%	47%	54%
Long COVID cases	15%	65%	75%	28%	33%
Deaths	45%	80%	86%	54%	62%
NHS resource use outcomes
GP visits	13%	65%	75%	27%	32%
Bed days in general ward	37%	78%	85%	48%	55%
Bed days in ICU	30%	78%	84%	47%	54%
Patient productivity loss
Total days lost	12%	64%	75%	26%	32%

Abbreviations: COVID-19, coronavirus disease 2019; GP, general practitioner; ICU, intensive care unit

^aNew outcomes (i.e. incidence) predicted for the period between 4 April 2022 and 2 April 2023

^bActual (Spring 2022) and anticipated (Autumn 2022) booster programs

^cAlternative Spring&Autumn₂₀₂₂ booster programs extending eligibility to individuals aged ≥ 5 years

^dAlternative Spring&Autumn₂₀₂₂ booster programs extending eligibility to individuals aged ≥ 5 years and assuming increased uptake among all age groups

^eAlternative Spring&Autumn₂₀₂₂ booster programs in which only individuals in Green Book [64] clinical risk groups would be eligible

^fAlternative Spring&Autumn₂₀₂₂ booster programs in which only individuals in Green Book [64] clinical risk groups would be eligible and assuming increased uptake in these groups

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Data availability statement

Data generated or analyzed during this study are available upon request.