Limitation:
There are some limitations in this study. Firstly, the patients could not be stratified by baseline mechanical ventilation assuming that tocilizumab efficacy is the same because of the low number of the included studies. Secondly, cohort studies are highly susceptible for confounding that may affect the internal validity of the treatment-effect relationship. Thirdly, immunomodulators such as steroids were given beyond tocilizumab in three studies (Guaraldi et al., 2020; Ip et al., 2020; Kewan et al., 2020) which could have an effect change. Finally, some other outcomes could not be combined due to difference in the follow-up time such as a rate of mechanical ventilation during 14 (Guaraldi et al., 2020), 21 (Kewan et al., 2020), and 28 days (Campochiaro et al., 2020).