Systematic Reviews
Copyright ©The Author(s) 2023. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Meta-Anal. Jun 18, 2023; 11(5): 167-180
Published online Jun 18, 2023. doi: 10.13105/wjma.v11.i5.167
Real-world effectiveness of mRNA COVID-19 vaccines in the elderly during the Delta and Omicron variants: Systematic review
Harvey Palalay, Riddhi Vyas, Barbara Tafuto
Harvey Palalay, Riddhi Vyas, Barbara Tafuto, Department of Health Informatics, Rutgers University, Piscataway, NJ 08854, United States
Author contributions: Palalay H conceived the manuscript from study design, literature search, study selection process, data extraction, analysis, and synthesis; Tafuto B reviewed the draft, added critical comment and intellectual content, and participated in most of the study steps; Vyas R provided additional input and guidance; All authors read and approved the final manuscript for submission and take full responsibility for the content.
Conflict-of-interest statement: No conflict of interest to declare.
PRISMA 2009 Checklist statement: The authors have read the PRISMA 2009 Checklist, and the manuscript was prepared and revised according to the PRISMA 2009 Checklist.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Harvey Palalay, MS, RN, Master's Student, Department of Health Informatics, Rutgers University, 675 Hoes Lane West, Piscataway, NJ 08854, United States. hkp48@shp.rutgers.edu
Received: January 28, 2023
Peer-review started: January 28, 2023
First decision: March 28, 2023
Revised: April 9, 2023
Accepted: April 18, 2023
Article in press: April 18, 2023
Published online: June 18, 2023
Processing time: 138 Days and 21.5 Hours
Abstract
BACKGROUND

As of 31 December 2022, there were over 6.6 million coronavirus disease 2019 (COVID-19) deaths and over 651 million cases across 200 countries worldwide. Despite the increase in vaccinations and booster shots, COVID-19 cases and deaths continue to remain high. While the effectiveness of these vaccines has already been established by different manufacturers, the fact remains that these vaccines were created quickly for global emergency use, tested under controlled clinical conditions from voluntary subjects and age groups whose general characteristics may differ from the actual general population.

AIM

To conduct a systematic review to determine the real-world effectiveness of mRNA COVID-19 vaccines in the elderly during the predominance of Delta and Omicron variants in preventing COVID-19 related infection, hospital, intensive care unit (ICU) admission and intubation, and death.

METHODS

A combination of Medical Subject Headings and non–Medical Subject Headings was carried out to identify all relevant research articles that meets the inclusion and exclusion criteria from PubMed, Cochrane, CINAHL, Scopus, ProQuest, EMBASE, Web of Science, and Google Scholar databases, as well as qualified research studies from pre–print servers using medRxiv and Research Square, published from January 1, 2021 - December 31, 2022.

RESULTS

As per the inclusion and exclusion criteria, the effectiveness of Pfizer-BioNTech and Moderna vaccines were evaluated from an estimated total study population of 26535692 using infection, hospital, ICU admission and intubation, and death as outcome measures from studies published between 2021 and 2022, conducted in New York, Finland, Canada, Costa Rica, Qatar, Greece, and Brazil. The risk of bias was evaluated using risk of bias in nonrandomized studies of interventions (ROBINS-I) tool for cohort, case-control, and cross-sectional studies. While clinical trial data on Pfizer-BioNTech and Moderna vaccines demonstrated 94% vaccine effectiveness in the elderly, the results in this study showed that vaccine effectiveness in real-world settings is marginally lower against infection (40%-89%), hospitalization (92%), ICU admission and intubation (98%-85%), and death (77%-87%) with an indication of diminished effectiveness of vaccine over time. Furthermore, 2 doses of mRNA vaccines are inadequate and only provides interim protection.

CONCLUSION

Because of the natural diminishing effectiveness of the vaccine, the need for booster dose to restore its efficacy is vital. From a research perspective, the use of highly heterogeneous outcome measures inhibits the comparison, contrast, and integration of the results which makes data pooling across different studies problematic. While pharmaceutical intervention like vaccination is important to fight an epidemic, utilizing common outcome measurements or carrying out studies with minimal heterogeneity in outcome measurements, is equally crucial to better understand and respond to an international health crisis.

Keywords: COVID-19; mRNA Vaccine; Effectiveness; Elderly; Delta; Omicron; Systematic review

Core Tip: This systematic review investigates the real-world effectiveness of mRNA coronavirus disease 2019 (COVID-19) vaccines in reducing morbidity and mortality in the elderly during the predominance of Delta and Omicron variants. This study found that the effectiveness of mRNA COVID-19 vaccines in the elderly against the Delta and Omicron variants is marginally lower than what was suggested in clinical trial data. Vaccine efficacy also diminishes over time, indicating the need for a booster dose to restore its effectiveness. Furthermore, to better understand and respond to an epidemic, studies should utilize common outcome measurements or minimize heterogeneity in outcome measures to facilitate data comparison and integration of results.