Poster Presentation Lorne Infection and Immunity 2023

COVID-19 in Brazil: Antibody Fc-dependent Mechanisms in Natural and Vaccine-Induced Immunity (#137)

Alexander Harris 1 2 , Liriye (Lydia) Kurtovic 1 2 , Shirley Lu 2 , D. Herbert Opi 1 2 3 , Heidi Drummer 2 , Bruce Wines 2 3 , Mark Hogarth 2 , Clarissa Valim 4 , Luís Cristóvão Porto 5 6 , James Beeson 1 2 3
  1. Department of Immunology, Monash University, Melbourne, Victoria, Australia
  2. Burnet Institute, Black Rock, VICTORIA, Australia
  3. Department of Medicine, Doherty Institute University of Melbourne, Melbourne, Victoria, Australia
  4. Boston University School of Public Health, Boston University, Boston, Massachusetts, USA
  5. Histocompatibility and Cryopreservation Laboratory, Institute of Biology Roberto Alcantara Gomes, UERJ, Rio de Janeiro, Brazil
  6. Clinical Pathology Service, Polyclinic Piquet Carneiro, UERJ, Rio de Janeiro, Brazil, Polyclinic Piquet Carneiro, UERJ, Rio de Janeiro, Brazil

Brazil has experienced a large COVID-19 burden, recording high levels of SARS-CoV-2 infections and deaths prior to the widespread deployment of vaccines. Natural infection and vaccination induce protective antibodies that can neutralise the virus or mediate other arms of the immune system by binding to Fcγ receptors (FcγR) on immune cells, facilitating phagocytosis and cell-killing, or by fixing the complement system. However, the induction and maintenance of Fc-dependent responses induced following natural infection and/or vaccination, especially in Brazil and with some vaccines, needs to be better defined.

In cohort studies in Brazil, we aimed to determine the magnitude and duration of FcγR-binding and complement-fixing antibodies targeting SARS-CoV-2 spike protein, elicited through natural infection or vaccination with the AstraZeneca or Sinovac vaccines, which have been widely deployed in Brazil. We also quantified the influence of prior SARS-CoV-2 infection on vaccine-induced antibody Fc-mediated functional activities. Serum samples were collected across multiple time points from Brazilian adults attending the UERJ Hospital with a SARS-CoV-2 infection (n=200) or for vaccination (n=222) with either the AstraZeneca or Sinovac vaccines (46.8% had a prior infection). Samples were tested for antibody FcγRI, FcγRIIa, and FcγRIIIa-binding, complement-fixation activity, and IgG against the SARS-CoV-2 spike protein.

AstraZeneca vaccination generally induced higher Fc-mediated functional responses compared to Sinovac vaccination and natural infection, which were comparable. Induction of complement-fixing antibodies was generally low. Vaccine-induced responses decayed substantially by 150 days. Vaccinees who had experienced SARS-CoV-2 infection prior to vaccination had substantially higher Fc-mediated functional antibodies than SARS-CoV-2 naïve adults. A greater magnitude of antibodies with Fc-mediated activities are induced by AstraZeneca vaccination in those who have previously experienced SARS-CoV-2 infection,

but antibodies decayed quickly over time. These findings are important in informing future vaccine design and optimal booster policy.