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

Table 1 Characteristic of studies included for vaccine effectiveness

Ref.	Study design	Location	Purpose	Age of study group	Vaccine type	Number of doses received	Variant of concern
Baum et al[33], 2022	Cohort study	Finland	To estimate VE against severe COVID-19 among the elderly	Adult population including ≥ 70 yr old	Pfizer-BioNTech	2 doses	Omicron
Grewal et al[34], 2022	Case control design	Canada	To estimate vaccine effectiveness of mRNA vaccines among aged ≥ 60 yr who were tested for SARS-CoV-2	≥ 60 yr old	Pfizer-BioNTech and Moderna	Booster	Omicron
Rosenberg et al[35], 2021	Cohort study	USA (NY)	To describe vaccine efficacy in NY	Adult population including ≥ 50 yr old	Pfizer-BioNTech and Moderna	2 doses	Delta
Rosero-Bixby[36], 2021	Cross-sectional study	Costa Rica	To estimate the dose-dependent effectiveness of coronavirus disease (COVID-19) vaccines to prevent severe illness in real-world conditions	Adult population including ≥ 58 yr old	Pfizer-BioNTech	2 doses	Delta
Rane et al[37], 2022	Case control study	USA (NY)	To monitor changes in vaccine effectiveness against COVID-19 outcomes for various vaccine products in different population subgroups	Adult population including ≥ 50 yr old	Pfizer-BioNTech	2 doses	Delta
Chemaitelly et al[38], 2021	Case control study	Qatar	To estimate vaccine effectiveness against any SARS-CoV-2 infection and against any severe, critical, or fatal case of COVID-19	Adult population including ≥ 50 yr old	Pfizer-BioNTech	2 doses	Delta
Lytras et al[39], 2022	Cohort study	Greece	To estimate COVID-19 effectiveness against disease and death	Adult population including ≥ 60 yr old	Pfizer-BioNTech and Moderna	2 doses and booster	Delta
Ranzani et al[40], 2022	Case control study	Brazil	To evaluate vaccine effectiveness against symptomatic COVID-19 and severe COVID-19 (hospital admission or deaths)	Adult population including ≥ 70 yr old	Pfizer-BioNTech	2 doses and booster	Omicron

COVID-19: Coronavirus disease 2019; SARS-CoV-2: Severe acute respiratory syndrome coronavirus 2; USA (NY): United States of America (New York); VE: Vaccine effectiveness.