Table 3. Relative vaccine effectiveness of fourth dose mRNA monovalent vaccines against hospitalisation, compared with third dose monovalent mRNA vaccines, 4 April–30 July 2022 (n = 864).

Characteristic	rVE (95% CI)	rOR (95% CI)	p value
Univariable logistic regression model
Fourth dose of monovalent mRNA vaccine	51.2 (32.1–65.0)	0.488 (0.350–0.679)	< 0.001
Multivariable logistic regression model
Fourth dose of monovalent mRNA vaccine	46.6 (13.9–67.1)	0.534 (0.329–0.861)	0.011
Time between third dose and admission	NA	1.004 (0.999–1.009)	0.13
Vaccine branda		0.980 (0.636–1.509)	> 0.9
Age		1.010 (0.981–1.039)	0.5
Sex (male)		1.139 (0.803–1.615)	0.5
CCI		0.972 (0.873–1.077)	0.6
IMD		0.974 (0.914–1.037)	0.4
LTCF Resident		0.443 (0.221–0.819)	0.014
Respiratory disease		0.640 (0.440–0.926)	0.019
Prevalenceb		1.001 (1.001–1.002)	< 0.001
Matched conditional logistic regression modelc
4th dose of monovalent mRNA vaccine	52.0 (20.9–70.9)	0.480 (0.291–0.791)	0.004
Time between third dose and admission	NA	1.005 (0.999–1.010)	0.088
Vaccine branda		1.002 (0.634–1.584)	> 0.9
Prevalenceb		1.002 (1.001–1.002)	< 0.001

CI: confidence interval; CCI: Charlson comorbidity index; LTCF: long-term care facility; IMD: index of multiple deprivation; NA: not applicable; rOR: relative odds ratio; rVE: relative vaccine effectiveness.

^a Vaccine brand of fourth dose of monovalent mRNA vaccine or third dose of monovalent mRNA vaccine (before last dose, any vaccine combination is considered), where 1 = SpikeVax and 0 = Comirnaty.

^b Prevalence was calculated on a daily basis.

^c 1:3 nearest neighbour propensity score matching with replacement (propensity score estimated using logistic regression on age, sex, CCI score, IMD, LTCF residency and respiratory disease), 179 test-positive cases were matched to 537 test-negative controls with no match found for 138 controls.