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

Table 8 Variations in best-adjusted effect estimates by level of adjustment, effect estimate type, location and study size

Factor/level	Endpoint	CP	H	IC	MV	S	M
	Population	T	CP	H	H	H	H
	Estimates	17	22	14	15	10	25
Estimates for closest to current smoking
Adjustment	U	0.55 (0.45-0.67)	1.44 (1.03-2.01)	1.16 (1.05-1.28)	1.16 (0.80-1.67)	1.17 (0.99-1.37)	1.52 (1.22-1.91)
	D	0.23 (0.09-0.59)	1.52 (1.18-1.95)	0.73 (0.56-0.96)	0.85 (0.67-1.07)	1.02 (0.89-1.16)	1.01 (0.87-1.17)
	C	0.58 (0.43-0.80)	0.96 (0.79-1.18)	0.81 (0.61-1.07)	0.99 (0.77-1.29)	1.23 (0.46-3.27)	1.09 (0.84-1.40)
	PC	-	-	-	-	0.71 (0.41-1.23)	-
	P	NS	< 0.05	< 0.001	NS	NS	< 0.05
Estimate type	OR	0.54 (0.46-0.63)	1.26 (0.97-1.64)	1.07 (0.87-1.32)	1.13 (0.88-1.44)	1.09 (0.93-1.27)	1.35 (1.07-1.70)
	RR	0.64 (0.31-1.34)	1.25 (1.20-1.31)	0.90 (0.71-1.15)	0.73 (0.56-0.95)	-	1.11 (0.87-1.40)
	HR	-	1.10 (0.97-1.24)	-	-	1.02 (0.64-1.63)	1.15 (0.89-1.50)
	P	NS	NS	NS	< 0.05	NS	NS
Location	United States	0.45 (0.37-0.54)	1.27 (1.11-1.46)	1.00 (0.81-1.22)	1.02 (0.83-1.26)	1.06 (0.72-1.56)	1.21 (0.95-1.53)
	Other	0.64 (0.55-0.73)	1.11 (0.48-2.57)	1.08 (0.79-1.49)	1.05 (0.65-1.71)	1.10 (1.02-1.17)	1.34 (1.07-1.69)
	P	< 0.01	NS	NS	NS	NS	NS
Study size	< 500	-	0.99 (0.58-1.69)	1.25 (0.91-1.71)	1.35 (1.02-1.80)	1.02 (0.65-1.59)	1.29 (0.97-1.72)
	500-	0.40 (0.27-0.61)	1.42 (1.17-1.72)	1.07 (0.69-1.65)	0.92 (0.34-2.46)	1.62 (1.14-2.29)	1.57 (1.20-2.05)
	5000-	0.51 (0.39-0.66)	1.43 (0.97-2.10)	0.64 (0.29-1.42)	0.83 (0.70-0.98)	0.81 (0.56-1.19)	1.03 (0.83-1.28)
	50,000+	0.67 (0.51-0.87)	1.00 (0.85-1.18)	0.97 (0.72-1.31)	0.98 (0.61-1.59)	1.09 (0.99-1.19)	0.94 (0.82-1.07)
	P	NS	< 0.05	NS	< 0.05	NS	< 0.01
Estimates for closest to ever smoking
Adjustment	U	0.67 (0.58-0.78)	1.71 (1.24-2.36)	1.19 (1.08-1.30)	1.24 (0.99-1.54)	1.14 (1.06-1.23)	1.79 (1.47-2.19)
	D	0.23 (0.09-0.59)	1.41 (1.04-1.92)	0.73 (0.56-0.96)	0.85 (0.67-1.07)	1.02 (0.89-1.16)	1.11 (0.81-1.53)
	C	0.77 (0.64-0.92)	0.93 (0.80-1.08)	1.01 (0.88-1.16)	1.04 (0.79-1.36)	1.35 (0.66-2.75)	1.12 (0.91-1.39)
	PC	-	-	-	-	0.71 (0.41-1.23)	-
	P	< 0.05	< 0.001	< 0.01	NS	NS	< 0.01
Estimate type	OR	0.67 (0.59-0.76)	1.39 (1.08-1.79)	1.16 (0.99-1.37)	1.14 (0.91-1.42)	1.10 (0.98-1.24)	1.53 (1.19-1.96)
	RR	0.87 (0.59-1.27)	1.25 (1.20-1.31)	1.01 (0.89-1.15)	1.02 (0.88-1.18)	-	1.16 (1.05-1.29)
	HR	-	1.03 (0.95-1.11)	-	-	1.02 (0.64-1.63)	1.28 (1.14-1.44)
	P	NS	< 0.001	NS	NS	NS	NS
Location	United States	0.65 (0.50-0.84)	1.38 (1.14-1.67)	1.10 (0.99-1.23)	1.08 (0.90-1.30)	1.15 (0.87-1.51)	1.43 (1.11-1.84)
	Other	0.74 (0.66-0.82)	1.31 (0.64-2.71)	1.08 (0.79-1.49)	1.05 (0.65-1.71)	1.10 (1.02-1.17)	1.43 (1.19-1.73)
	P	NS	NS	NS	NS	NS	NS
Study size	< 500	-	1.21 (0.84-1.75)	1.25 (0.93-1.69)	1.29 (0.95-1.76)	1.06 (0.74-1.52)	1.36 (1.05-1.75)
	500-	0.55 (0.37-0.80)	1.32 (0.99-1.76)	1.04 (0.92-1.18)	1.24 (0.77-2.00)	1.62 (1.14-2.29)	1.70 (1.34-2.16)
	5000-	0.64 (0.50-0.81)	1.71 (1.18-2.49)	1.48 (1.10-2.00)	0.83 (0.70-0.98)	1.00 (0.83-1.22)	1.27 (0.96-1.68)
	50000+	0.81 (0.73-0.89)	0.97 (0.88-1.07)	0.97 (0.73-1.28)	1.10 (0.79-1.52)	1.09 (0.99-1.19)	0.94 (0.82-1.07)
	P	< 0.05	< 0.01	NS	< 0.05	NS	< 0.001

The table shows effect estimates with 95% confidence interval. Variation between levels of a factor is coded as P < 0.001, P < 0.01, P < 0.05 or NS (P ≥ 0.05). C: Adjusted for comorbidities; CP: Coronavirus disease 2019 positive; D: Adjusted for demographics only; H: Hospitalized; HR: Hazard ratio; IC: Intensive care; M: Mortality; MV: Mechanical ventilation; OR: Odds ratio; PC: Adjusted for variables including post-coronavirus disease 2019 responses; RR: Relative risk; S: Severe coronavirus disease 2019; T: Tested for coronavirus disease 2019; U: Unadjusted.