Expert review of global real-world data on COVID-19 vaccine booster effectiveness and safety during the omicron-dominant phase of the pandemic

ABSTRACT

Introduction

COVID-19 vaccines have been highly effective in reducing morbidity and mortality during the pandemic. However, the emergence of the Omicron variant and subvariants as the globally dominant strains have raised doubts about the effectiveness of currently available vaccines and prompted debate about potential future vaccination strategies.

Areas covered

Using the publicly available IVAC VIEW-hub platform, we reviewed 52 studies on vaccine effectiveness (VE) after booster vaccinations. VE were reported for SARS-CoV-2 symptomatic infection, severe disease and death and stratified by vaccine schedule and age. In addition, a non-systematic literature review of safety was performed to identify single or multi-country studies investigating adverse event rates for at least two of the currently available COVID-19 vaccines.

Expert opinion

Booster shots of the current COVID-19 vaccines provide consistently high protection against Omicron-related severe disease and death. Additionally, this protection appears to be conserved for at least 3 months, with a small but significant waning after that. The positive risk-benefit ratio of these vaccines is well established, giving us confidence to administer additional doses as required. Future vaccination strategies will likely include a combination of schedules based on risk profile, as overly frequent boosting may be neither beneficial nor sustainable for the general population.

KEYWORDS:

• COVID-19
• omicron
• booster
• vaccine effectiveness
• waning immunity
• severe
• AZD1222
• mRNA
• CoronaVac

Article highlights

• All COVID-19 vaccines have a lower VE against symptomatic infection due to Omicron than to the Delta variant, even following a booster dose – VE significantly wanes within the first 3 months post-booster dose.

• Regardless of vaccine schedule, VE after a booster dose consistently prevented severe disease, hospital admission and death. VE against Omicron-related severe disease and death is high (85.4%) and is conserved for at least 3 months post-booster dose with a mean VE of 87.5% for 7-14 days post-booster, and a mean VE of 86.2% for 15-90 days post-booster. A small but significant waning of VE is seen more than 3 months post-booster compared to more than 7-14 and 15-90-days post-booster.

• We found no significant difference in booster VE among people with and without prior SARS-CoV-2 infection or between the general population and the elderly.

• VE against severe disease and death was comparable for both heterologous and homologous vaccine schedules amongst individuals who received a COVID-19 vaccine booster dose.

• There were no statistically significant differences between a three-dose mRNA homologous schedule and a three-dose AZD1222 homologous schedule or a two-dose Ad26.COV2.S homologous schedule.

• More studies in high-risk, comorbid, immunocompromised, and elderly populations, should be performed as a priority, as these are the most vulnerable to severe outcomes, particularly as the pandemic evolves into an endemic situation.

• Large population-level safety studies reinforce the overall, relative safety of the current vaccines in use globally, and emphasize the favorable risk-benefit profiles of all of these vaccines.

• Future vaccination strategies could incorporate annual booster shots for the general population alongside evaluation of the incremental benefits of the next generation of vaccines.

• Vaccination programs could include more regular, shorter interval, 4-6 monthly booster shots based on risk i.e. those who are elderly, and/or with comorbid conditions that increase the risk associated with a SARS-CoV-2 infection, as well as the use of a three-dose primary series to prolong the duration of protection, although data to support these recommendations is still lacking.

Acknowledgments

The authors wish to thank Shawna Tan of Medical Writers Asia for manuscript writing and Glen Halliwell and Sharon Pang of GCI Health for analysis of IVAC study and data visualizations.

Declaration of Interest

Following International Committee of Medical Journal Editors’ (ICMJE) guidelines, A Ong-Lim reports honoraria for lectures from Moderna and is a member of the Technical Advisory Group, Department of Health in the Philippines. C Alvarez-Moreno has received a grant from World Health Organization (WHO) to conduct the Solidarity Vaccine Trial in Colombia, he participates on the Colombian Data Safety Monitoring Board, and he reports receiving honoraria for lectures from Pfizer and AstraZeneca. C Huu Nghia, KP Hwang, R Solante, AJ. Rodriguez-Morales and S Chariyalertsak report consulting fees from AstraZeneca. J Ortiz Ibarra reports receiving consulting fees, meeting attendance support and speaker honoraria from AstraZeneca and meeting attendance support from Pfizer. D Do-Van reports consulting fees and honoraria for advisory board attendance by AstraZeneca. NC Chiu reports consulting fees from AstraZeneca and honoraria for scientific meeting travel and lecture from multiple companies. He is also a member of the Taiwan Vaccine Injury Compensation Program and Pediatric Infectious Disease Society of Taiwan. PI Lee reports grants from the Taiwan Center for Disease Control for COVID-19 vaccine immunogenicity studies, consulting fees from AstraZeneca, Merck Sharp & Dohme (MSD), and GlaxoSmithKline and payment for lectures from MSD. He also serves as the Chair, Advisory Committee on Immunization Practice in Taiwan. Prasad S. Kulkarni is employed by Serum Institute of India Pvt Ltd which manufactures a COVID-19 vaccine (Covishield) that is sub-licensed from AstraZeneca. R Crisenio Lobo reports consulting fees from AstraZeneca and honoraria for lectures from Menarini Philippines, Nestle, Mead Johnson, and Novartis. He is also the vice-chair of the National Adverse Events Following Immunization committee in the Philippines. S Kiertiburanakul reports consulting fees from AstraZeneca and honoraria for lectures from AstraZeneca, Pfizer and Zuellig Pharma. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/14760584.2023.2143347

Additional information

Funding

Funding for this manuscript was provided by AstraZeneca for medical writing support to summarize the International Vaccine Access Center (IVAC) data and develop draft visuals for review and interpretation by the authors. The authors were involved in the study design; in the interpretation of data; in reviewing the manuscript; and in the decision to submit the manuscript for publication. All authors had full access to all of the data in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis.