Effectiveness of vaccine combination

A study published in Nature shows that the combination of AstraZeneca and Pfizer vaccines confer better protection than 2 doses of Pfizer.

Key words: Vaccination, infection, efficacy, immune response, heterologous regimen, homologous regimen.


  • Patients vaccinated with the homologous regimen were twice as likely to be infected with SARS-CoV-2.

Description of the Study:

  • Title: Inmunogenicity and efficacy of heterologous ChAdOX1/BNT 162b2 vaccination
  • Principal investigators: Bruno Pozzetto, Vincent Legros, Sophia Djebali and Véronique Barateau.
  • Co-Investigadors: Nicolas Guibert, Marine Villard, Loïc Peyrot, Omran Allatif, Jean-Baptiste Fassier, Amélie Massardier-Pilonchéry, Karen Brengel-Pesce, Melyssa Yaugel-Novoa, Solène Denolly, Bertrand Boson, Thomas Bourlet, Antonin Bal, Martine Valette, Thibault Andrieu, Bruno Lina, Covid-Ser study group, François-Loïc Cosset, Stéphane Paul, Thierry Defrance, Jacqueline Marvel, Thierry Walzer, and Sophie Trouillet-Assant.
  • Centers of implementation: Hospices Civils de Lyon, CHU de Saint-Etienne, Université Claude Bernard Lyon 1, ENS de Lyon, Université Jean Monnet de Saint-Etienne, Inserm, CNRS and bioMérieux.
  • Study Poblation: Healthcare workers.
  • Study Type: Observational study.
  • Design: Two groups with different vaccination schedules.
  • Methods:
    – Statistical analysis of the risk of infection for both vaccination regimens, and comparison between them.
    – Blood tests to identify the immune response caused by both vaccination schedules.

Objectives of the Study:

Principal objective: Compare the risk of SARS-CoV-2 infection following heterologous ChAd / BNT or homologous BNT / BNT vaccination schedules.

Secondary objective: To study the difference in the immune response between the two study groups to understand the reason for the efficacy of each vaccination regimen.

More about this Study:

Context: After the adverse effects related to the AstraZeneca vaccine (ChAdOx1-S-nCoV-19), the High Health Authority recommended those under 55 years of age already vaccinated with a first dose of AstraZeneca, to be vaccinated with a second dose of any RNA vaccine, in this case, Pfizer (BNT162b2). This study investigates the differences between a heterologous ChAdOx1-S-nCoV-19 / BNT162b2 vaccination regimen and a homologous BNT162b2 / BNT162b2.

Hospices Civils de Lyon (HCL): Set of 13 public hospitals of excellence covering all medical and surgical disciplines in the Rhones-Alpes region.

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