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

Table 1 Main results for endpoint: Tested positive for coronavirus disease 2019

Selection of estimates1		Statistic2	Ever vs never	Current vs non-current	Current vs never	Former vs never	Closest to current	Closest to never
Population = general3
Best-adjusted	All	EE (95%CI)	1.04 (0.79-1.37)	0.76 (0.56-1.02)	0.87 (0.52-1.47)	1.09 (0.94-1.28)	0.78 (0.57-1.06)	0.89 (0.73-1.09)
		n	5	7	5	5	7	7
	C	EE (95%CI)	1.10 (0.70-1.72)	0.93 (0.43-2.01)	0.96 (0.42-2.17)	1.10 (0.86-1.40)	0.96 (0.42-2.17)	1.10 (0.70-1.72)
		n	3	3	3	3	3	3
	U	EE (95%CI)	0.71 (0.63-0.80)	0.56 (0.43-0.75)	0.45 (0.36-0.55)	0.92 (0.80-1.05)	0.56 (0.42-0.75)	0.65 (0.55-0.77)
		n	1	3	1	1	3	3
All estimates	U	EE (95%CI)	1.04 (0.83-1.29)	0.79 (0.51-1.22)	0.90 (0.46-1.78)	1.13 (0.97-1.31)	0.80 (0.53-1.22)	0.89 (0.74-1.08)
		n	5	7	5	5	7	7
Population = tested for COVID-194
Best-adjusted	All	EE (95%CI)	0.71 (0.60-0.84)	0.61 (0.52-0.71)	0.52 (0.43-0.64)	0.97 (0.86-1.09)	0.55 (0.47-0.65)	0.70 (0.63-0.77)
		n	10	13	8	8	17	17
	C	EE (95%CI)	0.77 (0.56-1.05)	0.60 (0.45-0.79)	0.53 (0.34-0.83)	0.90 (0.76-1.08)	0.58 (0.43-0.80)	0.77 (0.64-0.92)
		n	4	5	4	4	5	5
	U	EE (95%CI)	0.67 (0.52-0.86)	0.62 (0.51-0.75)	0.49 (0.42-0.58)	1.04 (0.85-1.28)	0.55 (0.45-0.67)	0.67 (0.58-0.78)
		n	6	8	4	4	11	11
All estimates	U	EE (95%CI)	0.72 (0.62-0.85)	0.61 (0.50-0.73)	0.53 (0.46-0.61)	0.97 (0.87-1.09)	0.55 (0.46-0.66)	0.71 (0.64-0.79)
		n	10	12	8	8	17	17

¹Best-adjusted = estimates for a study selected in preference order of adjustment (C = comorbidities, D = demographics only, U = unadjusted, P = includes post-coronavirus disease responses).

²EE: Effect estimate from random-effects meta-analysis.

³For population = general, the results are from six studies, one providing sex-specific estimates. Four provided odds ratio (OR)s, one hazard ratios and one relative risk (RR)s and ORs.

⁴For population = tested, the results are from 15 studies, two providing sex-specific estimates, with 13 providing only ORs and two RRs, one of these also providing ORs. COVID-19: Coronavirus disease 2019; CI: Confidence interval.