COVID-19 Antibody Responses after Vaccines and Infections

Several vaccines against COVID-19 have proven safe and effective in clinical trials. However, it is still not well understood how a prior SARS-CoV-2 infection affects the vaccine response and how long the protection provided by the vaccines lasts.

Otto O. Yang, University of California, Los Angeles, USA, and colleagues have compared antibody levels, quality, and persistence after one and two doses of an mRNA vaccine in individuals with or without a prior case of COVID-19. The researchers used an enzyme-linked immunosorbent assay (ELISA) to measure antibodies that target the receptor-binding domain (RBD), a part of the spike protein of SARS-CoV-2, in people who received the Pfizer/BioNTech or the Moderna vaccine, as well as in unvaccinated people soon after mild or severe COVID-19 cases.

In the participants without prior infection, one dose of either vaccine triggered antibody levels similar to those seen after mild COVID-19 infections, and two doses were required to obtain antibody levels close to those observed after severe cases. In contrast, in participants who had COVID-19 prior to vaccination, the first dose produced a vigorous antibody response similar to severe natural infection, but the second dose provided no additional increase in antibody levels. The potency of the antibodies, indicated by their ability to neutralize the SARS-CoV-2 spike protein, followed similar patterns.

After the second vaccine dose, antibody levels slowly dropped in both groups comparably to a natural infection, resulting in an average loss of 90 % within 85 days. The protection afforded by the vaccines might not be entirely based on antibodies, and more research on T-cell responses to the vaccines is needed. However, the results suggest that booster vaccinations will likely be required for everyone, according to the team. Overall, the results provide evidence that people who previously had COVID-19 need only one vaccine dose, uninfected individuals need two doses for full protection, and booster shots could be necessary for everyone in the future.

Primary, Recall, and Decay Kinetics of SARS-CoV-2 Vaccine Antibody Responses,
F. Javier Ibarrondo, Christian Hofmann, Jennifer A. Fulcher, David Goodman-Meza, William Mu, Mary Ann Hausner, Ayub Ali, Arumugam Balamurugan, Ellie Taus, Julie Elliott, Paul Krogstad, Nicole H. Tobin, Kathie G. Ferbas, Scott G. Kitchen, Grace M. Aldrovandi, Anne W. Rimoin, Otto O. Yang,
ACS Nano 2021.
https://doi.org/10.1021/acsnano.1c03972

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