Antibody Response against Circulating Omicron Variants 8 Months after the Third Dose of mRNA Vaccine

Abstract

The COVID-19 wave is being recently propelled by BA.2 and, particularly, BA.5 lineages, showing clear transmission advantages over the previously circulating strains. In this study, neutralizing antibody responses against SARS-CoV-2 Wild-Type, BA.2 and BA.5 Omicron sublineages were evaluated among vaccinees, uninfected or infected with Omicron BA.1 strain, 8 months after the third dose of SARS-CoV-2 vaccine. The aim of this study was to compare the cross-protective humoral response to the currently circulating variant strains induced by vaccination, followed by Omicron infection in some subjects. Results showed a low antibody titer against all three variants in uninfected vaccinated subjects. On the other hand, vaccinated subjects, infected with BA.1 variant after receiving the third dose (about 40 days later), showed a strong response against both BA.2 and BA.5 strains, albeit with lower titers. This reinforces the concept that vaccination is fundamental to induce an adequate and protective immune response against SARS-CoV-2, but needs to be updated, in order to also widen the range of action towards emerging variants, phylogenetically distant from the Wuhan strain, against which the current formulation is targeted.

Keywords: BA.2; BA.5; BNT162b2; Omicron; SARS-CoV-2; mRNA vaccine; mRNA-1273.

Figure 1

Immune response in vaccinated subjects, either infected with SARS-CoV-2 BA.1 variant or not. Anti-spike IgG antibody levels (Panel (a)) and neutralizing SARS-CoV-2 antibodies (Panel (b)) in serum samples of vaccinated subjects with three doses of mRNA vaccine, either infected (squares) or not (circles) with Omicron BA.1 strain. Differences in neutralizing IgG antibodies were evaluated against WT (red), BA.2 (blue), and BA.5 (green) strains (Panel (b)). In each plot, the horizontal line represents the mean (Panel (a)) or the geometric mean (Panel (b)), while the top and bottom lines show the 95% confidence interval (CI 95%). The p values are reported in the figures, where * stands for p ≤ 0.05, ** for 0.05< p <0.001 and *** stands for p < 0.001.