Table 2.

Effectiveness of the Vaccine in Preventing Severe COVID-19 Outcomes stratified according to different risk factors.

Risk factor	Hospitalization		Critical care admission		Death
	Effectiveness (%) (95% CI)	p value	Effectiveness (%) (95% CI)	p value	Effectiveness (%) (95% CI)	p value
Months		<0.001		<0.001		<0.001
Oct–Dec 2020 (wild-type virus)	97.5 (95.9, 98.4)		98.8 (95.3, 99.7)		100 (100, 100)
Jan–April 202 (alpha variant)	75.9 (73.4, 78.1)		81.2 (75.6, 85.5)		81.9 (66.8, 90.1)
May–July 2021 (delta variant)	41.8 (22.9, 56.0)		60.1 (9.4, 82.4)		62.7 (31.7, 79.6)
Comorbidity		<0.001		0.004		<0.001
Without any comorbidity	68.7 (63.9, 72.9)		76.4 (64.5, 84.3)		60.7 (12.2, 82.4)
With one or more comorbidities	83.5 (81.6, 85.3)		88.7 (84.8, 91.6)		97.1 (93.5, 98.7)
Ethnicity		0.58		0.65		0.51
Arab	79.3 (77.1, 81.3)		85.5 (80.8, 89.1)		85.6 (71.1, 92.8)
Non-Arab	80.4 (76.7, 83.6)		87.1 (79.9, 91.7)		76.9 (20.5, 93.3)
Age group		<0.001		0.61		0.24
≤60 years	84.7 (82.7, 86.4)		86.7 (81.8, 90.3)		92.3 (67.2, 98.2)
>60 years	68.4 (63.9, 72.3)		85 (78.3, 89.6)		80.1 (61.1, 89.8)
Gender		0.0003		0.0155		0.24
Female	82.3 (80, 84.3)		80.8 (73.1, 86.2)		77 (47.9, 89.8)
Male	75.5 (72.2, 78.5)		89.3 (85, 92.5)		88.9 (72.1, 95.6)

P values shown are for testing the interaction between each risk factor and vaccine status. Only statistically significant interactions (shown in bold) can be interpreted as significant subgroup differences. P < 0.05 are considered statistically significant.

P values were calculated using two-sided tests with no adjustment for multiple comparisons, and were computed using the Wald test on the interaction term in the Cox proportional hazard model. Non-Arab population includes Asian and other ethnicity groups as listed in Supplementary Table 11. CI Confidence Interval.