Predicting SARS-CoV-2 Variant Spread in a Completely Seropositive Population Using Semi-Quantitative Antibody Measurements in Blood Donors.
Buss L., Prete CA., Whittaker C., Salomon T., Oikawa MK., Pereira RHM., Moura ICG., Delerino L., Franca RFO., Miyajima F., Mendrone A., Almeida-Neto C., Salles NA., Ferreira SC., Fladzinski KA., de Souza LM., Schier LK., Inoue PM., Xabregas LA., Crispim MAE., Fraiji N., Carlos LMB., Pessoa V., Ribeiro MA., de Souza RE., Cavalcante AF., Valença MIB., da Silva MV., Lopes E., Filho LA., Mateos SOG., Nunes GT., Schlesinger D., da Silva SMN., Silva-Junior AL., Castro MC., Nascimento VH., Dye C., Busch MP., Faria NR., Sabino EC.
SARS-CoV-2 serologic surveys estimate the proportion of the population with antibodies against historical variants, which nears 100% in many settings. New approaches are required to fully exploit serosurvey data. Using a SARS-CoV-2 anti-Spike (S) protein chemiluminescent microparticle assay, we attained a semi-quantitative measurement of population IgG titers in serial cross-sectional monthly samples of blood donations across seven Brazilian state capitals (March 2021−November 2021). Using an ecological analysis, we assessed the contributions of prior attack rate and vaccination to antibody titer. We compared anti-S titer across the seven cities during the growth phase of the Delta variant and used this to predict the resulting age-standardized incidence of severe COVID-19 cases. We tested ~780 samples per month, per location. Seroprevalence rose to >95% across all seven capitals by November 2021. Driven by vaccination, mean antibody titer increased 16-fold over the study, with the greatest increases occurring in cities with the highest prior attack rates. Mean anti-S IgG was strongly correlated (adjusted R2 = 0.89) with the number of severe cases caused by Delta. Semi-quantitative anti-S antibody titers are informative about prior exposure and vaccination coverage and may also indicate the potential impact of future SARS-CoV-2 variants.