David Forgacs, Speaker at Vaccines Conferences
University of Georgia Center for Vaccines and Immunology, United States
Title : The effect of waning on antibody levels and the B cell recall response after SARS-CoV-2 vaccination and infection over time


Since the COVID-19 pandemic started in late 2019, there have been over 400 million reported cases of SARS-CoV-2 infections, and since the start of the vaccine rollouts in December 2020, over 4 billion people have been fully vaccinated with a COVID-19 vaccine. In order to longitudinally track the waning of SARS-CoV-2 antibody levels in people after vaccination and infection, we established the SPARTA (SeroPrevalence and Respiratory Tract Assessment) program, a large-scale sero-surveillance program in several locations across the United States. Having tracked 1,081 people for over a year, we found no significant decrease in antibody levels during the first 14 months after infection in unvaccinated participants, while there was significant waning in vaccinated participants regardless of previous infection status. Moreover, participants who were pre-immune to SARS-CoV-2 prior to vaccination seroconverted to significantly higher antibody levels, and their antibody levels stayed significantly higher than unvaccinated infected participants for the entire observation period. Participants who received a third (booster) dose of an mRNA vaccine not only increased their antibody levels 14-fold on average, but they also reached 3 times higher antibody levels than the peak of their antibody levels after being fully vaccinated. In order to ascertain whether the presence of serum antibodies is important for seroprotection, we have stimulated the memory B cells of 13 participants who lost all detectable circulating antibodies after vaccination or infection, and saw a significant recall response in the absence of serum antibodies in none of the three infected and only 70% of the ten vaccinated participants. This pattern suggests a strong correlation between humoral antibody levels and the effectiveness of the recall response, emphasizing the importance of booster vaccine doses.