Table 1

Characteristics of studies reviewed

StudyCountrySample size,
N
Diabetes, N (%)Hypertension, N (%)CVD, N (%)Pulmonary disease, N (%)Active smokers, N (%)Former
smokers, N (%)
ICU admission, N (%)Mortality, N (%)Notes
Original studies
Huang et al14
China418 (19.5)6 (14.6)6 (14.6)1 (2.4)3 (7.3)NR7 (17.1)6 (14.6)
Guan et al15
China108581 (7.5)165 (15.2)27 (2.5)12 (1.1)137 (12.6)21 (1.9)55 (5.0)15 (1.4)
Zhang et al16
China14017 (12.1)42 (30.0)12 (8.6)2 (1.4)2 (1.4)7 (5.0)
Yang
et al17
China529 (17.3)5 (9.6)4 (7.7)2 (3.8)NR52 (100.0)32 (61.5)
Mo et al18
China15515 (9.7)37 (21.9)15 (9.7)5 (3.2)6 (3.9)NR
Zhou et al19
China19136 (18.9)58 (30.4)15 (7.9)6 (3.1)11 (5.8)NR50 (26.2)54 (28.3)
Guo et al20
China18728 (14.9)61 (32.6)21 (11.2)18 (9.6)NR43 (23.0)
Richardson et al28
USA35671808 (50.7)3026 (84.8)966 (27.1)920 (25.8)558 (15.6)NR1281 (22.5)553 (9.7)
Goyal et al26
USA39399 (25.2)197 (50.1)82 (20.9)69 (17.6)20 (5.1)NR40 (10.2)
Qin et al21
China45275 (16.6)135 (29.9)27 (5.9)12 (2.7)7 (1.5)NR
Cummings et al27
USA25792 (35.8)162 (63.0)49 (19.1)24 (9.3)33 (12.8)*NR203 (79.0)101 (39.3)
Meta-analyses
Farsalinos et al22
China5960450 (7.6)35 (0.6)Pooled prevalence of smokers among hospitalised patients with COVID-19 in China was 6.5% (95% CI 4.9% to 8.2%)
Lippi et al40
China1399No significant association between active smoking and COVID-19 severity (OR 1.69 (0.41 to 6.92); p=0.254)
Preprints
Miyara et al24
France482102/473158/47329/47334/473285/473Daily smokers have lower probability of developing severe COVID-19 when compared with the general population
OpenSAFELY Collaborators31
UK17 425 455489 297 (2.8)5 962 122 (34.2)1 173 433 (6.7)707 284 (4.1)2 962 373 (17.0)5 737 545 (32.9)5683 (0.03)On adjustment for multiple covariates, smoking was associated with a reduced risk for COVID-19 mortality (OR 0.88 (0.79 to 0.99))
  • *Study reported ‘current or former smokers’.

  • CI, Confidence interval; CVD, cardiovascular disease; ICU, Intensive care unit; NR, not reported; OR, Odds ratio; UK, United Kingdom; USA, United States of America.