Real-world effectiveness of mRNA COVID-19 vaccines in the elderly during the Delta and Omicron variants: Systematic review

Table 3 ROBINS-I risk of bias assessment of observational studies

Ref.	Confounding	Selection of participants	Classification of interventions	Deviations from interventions	Missing data	Measurement of outcomes	Reported result	Overall bias
Baum et al[33], 2022	Moderate	Low	Moderate	Moderate	Low	Low	Low	Moderate
Grewal et al[34], 2022	Moderate	Moderate	Low	Low	Low	Low	Low	Moderate
Rosenberg et al[35], 2021	Moderate	Moderate	Low	Low	Moderate	Low	Low	Moderate
Rosero-Bixby[36], 2021	Moderate	Low	Low	Low	Moderate	Moderate	Low	Moderate
Rane et al[37], 2022	Low	Low	Low	Low	Moderate	Low	Low	Low
Chemaitelly et al[38], 2021	Moderate	Low	Low	Low	Moderate	Low	Low	Moderate
Lytras et al[39], 2022	Moderate	Low	Low	Low	Moderate	Moderate	Low	Moderate
Ranzani et al[40], 2022	Low	Low	Low	Low	Low	Moderate	Low	Moderate

Low risk: Comparable to a well-performed randomised trial; Moderate risk: Sound for a non-randomised study but cannot be compared to a well performed randomised trial; Serious risk: Study has some important problems; Critical risk: Study is too problematic to provide any useful evidence.