Systematic review with meta-analysis of the epidemiological evidence in Europe, Israel, America and Australasia on smoking and COVID-19

Table 5 Results for endpoint: Severe coronavirus disease 2019¹

Selection of estimates2			Statistic3	Ever vs never	Current vs non-current	Current vs never	Former vs never	Closest to current	Closest to ever
Population = positive4
Best-adjusted	All		EE (95%CI)	1.39 (1.07-1.80)	1.04 (0.91-1.20)	1.27 (0.82-1.95)	1.20 (0.62-2.32)	1.10 (0.97-1.25)	1.10 (0.97-1.25)
			n	7	5	4	4	8	8
	C		EE (95%CI)	-	1.02 (0.88-1.18)	-	-	1.02 (0.88-1.18)	1.02 (0.88-1.18)
			n	0	1	0	0	1	1
	U		EE (95%CI)	1.30 (0.94-1.79)	1.26 (0.82-1.93)	1.27 (0.82-1.95)	1.20 (0.62-2.32)	1.35 (0.95-1.92)	1.30 (0.94-1.79)
			n	5	4	4	4	5	5
All estimates	U		EE (95%CI)	1.63 (1.27-2.10)	1.17 (1.09-1.25)	1.27 (0.82-1.95)	1.20 (0.62-2.32)	1.48 (1.13-1.94)	1.45 (1.12-1.86)
			n	7	5	4	4	8	8
Population = hospitalized5
Best-adjusted		All	EE (95%CI)	1.15 (0.87-1.51)	1.05 (0.93-1.18)	0.74 (0.49-1.12)	1.07 (0.87-1.32)	1.08 (0.94-1.25)	1.09 (0.98-1.22)
			n	7	5	2	2	10	10
		C	EE (95%CI)	1.35 (0.66-2.75)	0.76 (0.50-1.15)	0.77 (0.51-1.17)	1.06 (0.86-1.31)	1.23 (0.46-3.27)	1.35 (0.66-2.75)
			n	2	1	1	1	2	2
		U	EE (95%CI)	1.38 (1.04-1.83)	1.12 (1.04-1.21)	0.29 (0.03-2.64)	1.25 (0.56-2.76)	1.17 (0.99-1.37)	1.14 (1.06-1.23)
			n	4	3	1	1	6	6
All estimates		U	EE (95%CI)	1.40 (1.20-1.63)	1.14 (1.04-1.24)	0.89 (0.54-1.46)	1.48 (1.23-1.80)	1.17 (1.08-1.27)	1.21 (1.12-1.29)
			n	6	5	2	2	9	9

¹In most studies the endpoint was severe coronavirus disease 2019 (COVID-19) as defined by the author, but it was admitted to ICU or died in two studies, pneumonia in one, increased oxygen required in one and COVID-19 progressed in one.

²Best-adjusted = estimates for a study selected in preference order of adjustment (C = comorbidities, U = unadjusted, P = includes post-COVID responses).

³EE = effect estimate from random-effects meta-analysis.

⁴For population = positive, the results are from five studies, one study providing four estimates by age and sex. All estimates are odds ratio (OR)s.

⁵For population = hospitalized, the results are from 10 studies, nine providing ORs and one relative risks and hazard ratios. COVID-19: Coronavirus disease 2019; CI: Confidence interval.