TABLE 4.

Vaccine effectiveness against hospitalization and against hospitalization or death, by vaccine number and type, during the Omicron-dominant period December 20, 2021, to March 31, 2022

Vaccination status	Person-years	Hospitalizations within 14 d of SARS-CoV-2 positive infection	Deaths within 28 d of SARS-CoV-2 positive infection	Hospitalizations within 14 d or deaths within 28 d of SARS-CoV-2 positive infection	Risk-adjusted hospitalization incidence rate ratio (hospitalization within 14 d of SARS-CoV-2 positive infection)	P	Risk-adjusted hospitalization or death incidence rate ratio (hospitalization within 14 d or death within 28 d of SARS-CoV-2 positive infection)	P
Unvaccinated	497	38	10	43	–		–
Two doses	870.5	82	13	92	1.27 (0.86-1.88)	0.2	1.27 (0.88-1.83)	0.2
Three doses	6793	341	106	389	0.66 (0.46-0.93)	0.02	0.62 (0.45-0.86)	0.004
Four doses	1983	54	14	63	0.43 (0.27-0.66)	<0.0001	0.39 (0.26-0.58)	<0.0001
By vaccine type
Unvaccinated	497	38	10	43	–		–
AZ spine only	520.5	52	8	57	1.36 (0.89-2.07)	0.2	1.32 (0.89-1.97)	0.2
mRNA spine only	350	30	5	35	1.15 (0.71-1.86)	0.6	1.19 (0.76-1.87)	0.4
AZ spine + mRNA booster	3944.4	194	65	220	0.66 (0.46-0.94)	0.02	0.62 (0.44-0.87)	0.01
mRNA spine + mRNA booster	2848.6	147	41	169	0.65 (0.45-0.94)	0.02	0.62 (0.44-0.88)	0.01
AZ spine + 2 mRNA boosters	1055.8	32	8	36	0.48 (0.29-0.79)	0.004	0.42 (0.27-0.67)	<0.0001
mRNA spine + 2 mRNA boosters	927.1	22	6	27	0.36 (0.21-0.63)	<0.0001	0.35 (0.21-0.57)	<0.0001

“–” represents ‘Not relevant’ in this context.

AZ, ChAdOx1-S vaccine; mRNA, BNT162b2 or mRNA-1273 vaccines; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.