Evaluation of the Real-World Effectiveness of Vaccines against COVID-19 at a Local Level: Protocol for a Test-Negative Case-Control Study

Cátia Brazete; Marta Pinto; Lígia Sá; Ana Aguiar; Filipe Alves; Raquel Duarte

doi:10.3390/vaccines10050822

Evaluation of the Real-World Effectiveness of Vaccines against COVID-19 at a Local Level: Protocol for a Test-Negative Case-Control Study

Vaccines (Basel). 2022 May 23;10(5):822. doi: 10.3390/vaccines10050822.

Authors

Cátia Brazete^{1

2}, Marta Pinto^{3

4}, Lígia Sá², Ana Aguiar^{1

5}, Filipe Alves³, Raquel Duarte^{1

3

5

6

7}

Affiliations

¹ EPIUnit-Instituto de Saúde Pública, Universidade do Porto, 4050-600 Porto, Portugal.
² Unidade de Saúde Pública do Alto Minho, 4904-459 Viana do Castelo, Portugal.
³ Unidade de Investigação Clínica da ARS Norte, 4000-477 Porto, Portugal.
⁴ Faculdade de Psicologia e Ciências da Educação, Universidade do Porto, 4200-135 Porto, Portugal.
⁵ Laboratório Para a Investigação Integrativa e Translacional em Saúde Populacional (ITR), 4050-600 Porto, Portugal.
⁶ Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, 4050-303 Porto, Portugal.
⁷ Serviço de Pneumologia, Centro Hospitalar de Vila Nova de Gaia/Espinho, 4434-502 Vila Nova de Gaia, Portugal.

Abstract

Vaccines against COVID-19 approved for use in the EU/EEA have been shown to be highly effective against wild-type SARS-CoV-2. However, their effectiveness against new variants may be reduced. This study aims to evaluate the effectiveness of vaccines against COVID-19 in the prevention of symptomatic and severe disease, during pre- and post-omicron phases. Individuals who sought treatment at the emergency department of a Portuguese hospital with COVID-19-like disease and were tested for SARS-CoV-2 are the subjects of the study. Patients who received a positive result are considered cases, while those with negative results are the controls. The test-negative case-control method is one of the study designs recommended by WHO to estimate the effectiveness of vaccines against COVID-19. The main advantage of this design is that it controls for the healthcare seeking bias, commonly present in traditional cohort and case-control designs. This study may have broad implications for understanding the real-world performance of the COVID-19 vaccines at the local level, which may play a key role in promoting adherence to vaccination. Moreover, this study may contribute to inform decisions regarding booster doses and variant-specific vaccine formulations leading to the control of this and future pandemics.

Keywords: COVID-19 vaccines; case–control studies; district hospitals; effectiveness.

Grants and funding

Ana Aguiar holds a PhD grant (Reference: 2020.09390.BD), co-funded by the Fundação para a Ciência e a Tecnologia (FCT) and the Fundo Social Europeu (FSE) Program.