Public health impact of booster vaccination against COVID-19 in the UK during Delta variant dominance in autumn 2021

Figures & data

Figure 1. Dynamic transmission model diagram. Compartments—all compartments are further stratified by age: S—susceptible. V_1,2,B—vaccinated with dose 1, 2 and booster. E—Exposed, unvaccinated. EV_1,2,B—exposed and vaccinated by dose 1, 2 and booster. I_{S, V1S, V2S, VBS}—infectious with symptoms 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}—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 effectiveness and duration inputs.

Vaccine	Effectiveness against infection	Source	Effectiveness against hospitalization	Source	Mean duration of protection^a	Source
Dose 1	50.5%	^29^a	86.6%	^30^a	6 months	assumed
Dose 2	74.5%	^29^a	94.9%	^30^a	6 months	assumed
Booster	94.0%	^31^a	97.0%	^31^a	6 months	assumed

^aBrand-agnostic vaccine effectiveness calculated from UK data for vaccine-specific effectiveness estimates, and weighted by vaccine uptake.

Table 2. Health inputs for model population infected with COVID-19.

	Age group (years)
	0–4	5–9	10–19	20–29	30–39	40–49	50–59	60–69	70–79	80+	All ages^b	Source
Probability of symptoms (%)	40	40	25	37	42	51	59	72	76	76	–	Derived from Refs.^37^,^38
Reduction in probability of symptoms^a,b (%)
Dose 1	–	–	–	–	–	–	–	–	–	–	5.9	^19
Dose 2	–	–	–	–	–	–	–	–	–	–	19.1	^19
Booster	–	–	–	–	–	–	–	–	–	–	6.0	^31
Proportion hospitalized^c (%)	4.1	1.3	2.2	2.8	3.5	4.5	8.1	16.2	48.1	68.6	–	^27
Proportion hospitalized in ICU (%)	0.0	0.0	0.0	12.0	22.0	31.0	31.0	29.0	12.0	2.0	–	^d
Incident fatality rate^c (%)	0.002	0.008	0.016	0.070	0.112	0.467	0.728	1.155	4.003	6.382	–	^27
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	–	^39^e
Risk ratio of hospitalization^b	–	–	–	–	–	–	–	–	–	–	1.70	^40
Risk ratio of ICU admission^b	–	–	–	–	–	–	–	–	–	–	1.12	^41
Risk ratio of mortality ^b	–	–	–	–	–	–	–	–	–	–	2.15	^40^f
Patients with PASC^b (%)
Non-hospitalized and symptomatic	–	–	–	–	–	–	–	–	–	–	32	^42
Hospitalized	–	–	–	–	–	–	–	–	–	–	51	^42

Abbreviations. COVID-19, Coronavirus disease 2019; ICNARC, Intensive Care National Audit & Resource Centre; ICU, Intensive care unit; PASC, Post-acute sequelae of COVID-19; PHE, Public Health England.

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

^bAssumed to be the same across all age groups.

^cSymptomatic cases only.

^dDerived from the ICNARC report of overall probability of being admitted to an ICU and the age distribution of cases in ICU, considering the age distribution of hospitalized cases from PHE data.

^ePopulation-size weighted average of point prevalence for each age.

^fDerived from the reported cases, deaths, and probabilities for symptomatic patients (see Supplementary Table 2).

Figure 2. Modelled new weekly COVID-19 cases with and without booster vaccination. Base case estimation of new weekly COVID-19 cases per 100,000 population over the model time horizon, with (green) or without (grey) booster vaccination.

Table 3. Base case outcomes and difference with UK booster vaccination program.

​	Booster​	No booster​	Absolute difference​	Difference (%)​
Health outcomes
COVID-19 cases​	2,947,417	3,494,823	−547,406	−16
Hospitalizations​	80,778	116,913	−36,135	−31
COVID-19 deaths​ ​	11,264	15,464	−4,200	−27
PASC cases	573,044	720,324	−147,280	−20
NHS healthcare resource use​
General ward admissions	66,706	96,979	−30,273	−31
ICU admissions	14,072	19,934	−5,862	−29
Bed-days in general ward	567,001	824,319	−257,318	−31
Bed-days in ICU	141,563	200,538	−58,975	−29
GP visits	1,120,159	1,348,958	−228,799	−17
Productivity loss
Days of paid and unpaid work lost	75,128,781	91,625,390	−16,496,609	−18

Abbreviations. COVID-19, Coronavirus disease 2019; GP, General practitioner; ICU, Intensive care unit; NHS, National Health Service; PASC, Post-acute sequalae of COVID-19.

Table 4. Averted health outcomes and resource use savings with booster vaccination in base case and hypothetical scenarios.

	Base case - absolute difference^a, (% difference^b)	Hypothetical scenarios - absolute difference^a,(% difference^b)
		Scenario 1.1 Coverage ↑^c Infectivity ─ Severity ─	Scenario 1.2 Coverage ─ Infectivity ↑ Severity ↓	Scenario 1.3 Coverage ↑^c Infectivity ↑ Severity ↓	Scenario 1.4 Coverage ─ Infectivity ↓ Severity ─	Scenario 1.5 Coverage ↑^c Infectivity ↓ Severity ─	Scenario 1.6 Pediatric primary series^d	Scenario 2 Extended time horizon
Health outcomes
COVID-19 cases	−547,406​ (−16%)	−1,437,977 (−41%)	−11,516,004 (−10%)	−35,049,305 (−31%)	−10,730 (−4%)	−44,138 (−15%)	−1,898,365 (−64%)	−7,741,155 (−47%)
Hospitalizations	−36,135 (−31%)	−61,619 (−53%)	−77,998 (−7%)	−144,408 (−14%)	−613 (−13%)	−1,442 (−29%)	−51,215 (−63%)	−599,992 (−65%)
COVID-19 deaths	−4,200​ (−27%)	−7,648 (−49%)	−109,649 (−20%)	−228,244 (−42%)	−109 (−5%)	−273 (−12%)	−5,412 (−48%)	−58,722 (−62%)
PASC cases	−147,280 (−20%)	−356,664 (−50%)	−3,624,172 (−12%)	−10,906,503 (−36%)	−3,121 (−6%)	−12,230 (−23%)	−329,009 (−57%)	−2,069,307 (−54%)
NHS healthcare resource use​
General ward admissions	−30,273 (−31%)	−51,035 (−53%)	−70,836 (−8%)	−128,798 (−14%)	−513 (−12%)	−1,184 (−29%)	−42,424 (−64%)	−501,438 (−65%)
ICU admissions	−5,862 (−29%)	−10,584 (−53%)	−7,162 (−5%)	−15,610 (−11%)	−101 (−13%)	−259 (−33%)	−8,790 (−62%)	−98,554 (−63%)
Bed-days in general ward	−257,318 (−31%)	−433,800 (−53%)	−602,104 (−8%)	−1,094,786 (−14%)	−4,358 (−12%)	−10,061 (−29%)	−360,608 (−64%)	−4,262,221 (−65%)
Bed-days in ICU	−58,975 (−29%)	−106,475 (−53%)	−72,048 (−5%)	−157,033 (−11%)	−1,015 (−13%)	−2,607 (−33%)	−88,430 (−62%)	−991,453 (−63%)
GP visits	−228,799 (−17%)	−580,234 (−43%)	−5,503,705 (−11%)	−15,632,369 (−31%)	−4,682 (−4%)	−18,272 (−17%)	−705,045 (−63%)	−3,169,504 (−48%)
Productivity loss
Days of paid and unpaid work lost	−16,496,609 (−18%)	−44,219,529 (−48%)	−322,862,293 (−9%)	−1,185,708,106 (−33%)	−338,103 (−5%)	−1,538,337 (−22%)	−43,472,406 (−58%)	−237,012,273 (−52%)

Abbreviations. COVID-19, Coronavirus disease 2019; GP, General practitioner; ICU, Intensive care unit; NHS, National Health Service; PASC, Post-acute sequalae of COVID-19.

^aDifference using scenario-specific estimates: booster vaccination minus no booster vaccination.

^bPercentage difference from scenario-specific estimate for no booster vaccination, unless otherwise stated.

^cAccelerated coverage reaching maximum coverage rates in four weeks.

^dAbsolute difference and percentage difference compared to base case booster (observed adult booster program).

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Data availability statement

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