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).