• Thiago Cerqueira-Silva, Syed Ahmar Shah, Chris Robertson, Mauro Sanchez, KatikireddiSrinivasa VittalSV0000-0001-6593-9092Public Health Scotland, Glasgow, United Kingdom.MRC/CSO Social & Public Health Sciences Unit, University of Glasgow, Glasgow, United Kingdom., de Araujo OliveiraViniciusV0000-0001-7858-9650Universidade Federal de Bahia (UFBA), Salvador, Bahia, Brazil.Center for Data Integration and Knowledge for Health (Cidacs), Instituto Gonçalo Moniz, Fiocruz, Salvador, Bahia, Brazil., Enny S Paixão, Igor Rudan, Juracy Bertoldo Junior, Gerson O Penna, Neil Pearce, Guilherme Loureiro Werneck, Mauricio L Barreto, Viviane S Boaventura, Aziz Sheikh, and Manoel Barral-Netto.
• LIB and LEITV Laboratories, Instituto Gonçalo Moniz, Fiocruz, Salvador, Bahia, Brazil.
• PLoS Med. 2023 Jan 1; 20 (1): e1004156e1004156.

BackgroundBrazil and Scotland have used mRNA boosters in their respective populations since September 2021, with Omicron's emergence accelerating their booster program. Despite this, both countries have reported substantial recent increases in Coronavirus Disease 2019 (COVID-19) cases. The duration of the protection conferred by the booster dose against symptomatic Omicron cases and severe outcomes is unclear.Methods And FindingsUsing a test-negative design, we analyzed national databases to estimate the vaccine effectiveness (VE) of a primary series (with ChAdOx1 or BNT162b2) plus an mRNA vaccine booster (with BNT162b2 or mRNA-1273) against symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and severe COVID-19 outcomes (hospitalization or death) during the period of Omicron dominance in Brazil and Scotland compared to unvaccinated individuals. Additional analyses included stratification by age group (18 to 49, 50 to 64, ≥65). All individuals aged 18 years or older who reported acute respiratory illness symptoms and tested for SARS-CoV-2 infection between January 1, 2022, and April 23, 2022, in Brazil and Scotland were eligible for the study. At 14 to 29 days after the mRNA booster, the VE against symptomatic SARS-CoV-2 infection of ChAdOx1 plus BNT162b2 booster was 51.6%, (95% confidence interval (CI): [51.0, 52.2], p < 0.001) in Brazil and 67.1% (95% CI [65.5, 68.5], p < 0.001) in Scotland. At ≥4 months, protection against symptomatic infection waned to 4.2% (95% CI [0.7, 7.6], p = 0.02) in Brazil and 37.4% (95% CI [33.8, 40.9], p < 0.001) in Scotland. VE against severe outcomes in Brazil was 93.5% (95% CI [93.0, 94.0], p < 0.001) at 14 to 29 days post-booster, decreasing to 82.3% (95% CI [79.7, 84.7], p < 0.001) and 98.3% (95% CI [87.3, 99.8], p < 0.001) to 77.8% (95% CI [51.4, 89.9], p < 0.001) in Scotland for the same periods. Similar results were obtained with the primary series of BNT162b2 plus homologous booster. Potential limitations of this study were that we assumed that all cases included in the analysis were due to the Omicron variant based on the period of dominance and the limited follow-up time since the booster dose.ConclusionsWe observed that mRNA boosters after a primary vaccination course with either mRNA or viral-vector vaccines provided modest, short-lived protection against symptomatic infection with Omicron but substantial and more sustained protection against severe COVID-19 outcomes for at least 3 months.Copyright: © 2023 Cerqueira-Silva et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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