Demonstration of Antibodies Against SARS-CoV-2, Neutralizing or Binding, in Seroconversion Panels After mRNA-1273, BNT-162b2, and Ad26.COV2.S Vaccine Administration

Vaccines are an important tool in combating the COVID-19 pandemic. Two mRNA vaccines (mRNA-1273 and BNT-162b2) and an adenovirus vector vaccine (Ad26.COV2.S) were among the first vaccines to be approved by global regulatory authorities. The aim of this observational study was to characterize the levels and time course of the generation of anti-SARS-CoV-2 spike protein antibodies after vaccination with 3 different vaccines and the neutralizing activity of these antibodies. Seroconversion panels were generated from blood samples collected before and after vaccination with 3 COVID-19 vaccines: mRNA-1273, BNT-162b2, and Ad26.COV2.S. The seroconversion panels were tested for antibody activity by chemiluminescent immunoassay or enzyme-linked immunosorbent assay (ELISA), and 1 panel was tested for neutralization activity in a pseudovirus assay. Participants positive for anti-SARS-CoV-2 antibodies before vaccination (18.6%) had a higher response to the first dose than participants who tested negative. For 2-dose vaccines, older participants showed a lower response to the first dose than younger participants. All participants showed positive responses after the second vaccine. For the adenovirus vector vaccine, 2 participants did not generate antibody responses after vaccination. Four participants were negative at 2 weeks but positive at 2 months. Pseudovirus neutralization showed good correlation with antibody activity (correlation coefficient = 0.78, P < .0001). Antibody responses in participants over 45 years old tended to be less robust. Participants that had been infected with SARS-CoV-2 and had antibodies prior to vaccination showed a more robust response to initial vaccination. Older participants (>45 years) showed less robust responses to both types of vaccine. All participants receiving full mRNA vaccination showed positive antibody responses. Some participants receiving the adenovirus vaccine did not respond. Antibody responses correlated well with neutralization activity. Seroconversion panels can be useful in the development of antibody assays and in investigating their effectiveness against new SARS-CoV-2 variants.