Effectiveness of ChAdOx1 vaccine in elderly in SARS-CoV-2 Gamma variant transmission in Brazil

 Matt Hitchings, Otavio T Ranzani, Murilo Dorion, Tatiana Lang D'Agostini, Regiane Cardoso de Paula, Olivia Ferreira Pereira de Paula, Edlaine Faria de Moura Villela, Mario Sergio Scaramuzzini Torres, Silvano Barbosa de Oliveira, Wade Schulz, Maria Almiron, Rodrigo Said, Roberto Dias de Oliveira, Patricia Vieira da Silva, Wildo Navegantes de Araújo, Jean Carlo Gorinchteyn, Jason R Andrews, Derek A.T. Cummings, Albert Ko, Julio Croda

doi: https://doi.org/10.1101/2021.07.19.21260802

This article is a preprint and has not been certified by peer review [what does this mean?]. It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice.

PDF: https://www.medrxiv.org/content/10.1101/2021.07.19.21260802v1.full.pdf

Abstract

Background A two-dose regimen of ChAdOx1 coronavirus disease 19 (Covid-19) vaccine with an inter-dose interval of three months has been implemented in many countries with restricted vaccine supply. However, there is limited evidence for the effectiveness of ChAdOx1 by dose in elderly populations in countries with high prevalence of the Gamma variant of severe acute respiratory syndrome 2 (SARS-CoV-2). Methods We conducted a test-negative case-control study to estimate the effectiveness of ChAdOx1 vaccine in adults aged 60 years or older during a Gamma-variant-associated epidemic in São Paulo state, Brazil, between 17 January and 2 July 2021. Cases and matched test-negative controls were individuals, identified from surveillance databases, who experienced an acute respiratory illness and underwent SARS-CoV-2 RT-PCR testing. We used conditional logistic regression to estimate the effectiveness by dose against RT-PCR-confirmed Covid-19, Covid-19 hospitalization, and Covid-19-related death. Results 61,164 individuals were selected into matched case-control pairs. Starting ≥28 days after the first dose, adjusted effectiveness of a single dose of ChAdOx1 was 33.4% (95% CI, 26.4 to 39.7) against Covid-19, 55.1% (95% CI, 46.6 to 62.2) against hospitalization, and 61.8% (95% CI, 48.9 to 71.4) against death. Starting ≥14 days after the second dose, the adjusted effectiveness of the two-dose schedule was 77.9% (95% CI, 69.2 to 84.2) against Covid-19, 87.6% (95% CI, 78.2 to 92.9) against hospitalization, and 93.6% (95% CI, 81.9 to 97.7) against death. Conclusions Completion of the ChAdOx1 vaccine schedule afforded significantly increased protection over a single dose against mild and severe Covid-19 outcomes in elderly individuals during widespread Gamma variant transmission.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

We are grateful for the Pan American Health Organization's support and the São Paulo State in making the databases available for analysis. JC is supported by the Oswaldo Cruz Foundation (Edital Covid-19 - resposta rápida: 48111668950485). OTR is funded by a Sara Borrell fellowship (CD19/00110) from the Instituto de Salud Carlos III. OTR acknowledges support from the Spanish Ministry of Science and Innovation through the Centro de Excelencia Severo Ochoa 2019-2023 Program and from the Generalitat de Catalunya through the CERCA Program.

https://www.medrxiv.org/content/10.1101/2021.07.19.21260802v1