Anti-SARS-CoV-2 Omicron BA.5 RBD antibody titers generated by the protein subunit vaccine Abdala in breast milk

Objective

In this work, we investigate the presence of antibodies against OmicronBA.5 RBD in breast milk from puerperal women, vaccinated during pregnancy with the protein subunit vaccine Abdala, based on the Wuhan-Hu-1 RBD.

Materials and methods

Breast milk samples were collected between September 30 and November 25, 2021, from 2 groups of participants: 5- and 9-weeks after the third dose of the vaccine. Antibody titers against OmicronBA.5 RBD and Wuhan-Hu-1 RBD were evaluated simultaneously by a homemade ELISA. The relationship of antibody titers with the parity at the beginning of vaccination and with the participants health status was assessed.

Results

Binding of OmicronBA.5 RBD, such as Wuhan-Hu-1, to IgA and IgG antibodies was detected in all breast milk samples, although the anti-RBD-Wuhan-Hu-1 titers were higher. The immune response to OmicronBA.5 could be related to the glycosylation of the Abdala RBD, expressed in Pichia pastoris, which contributes to the immunogenicity and to the exposure of epitopes that are conserved in pandemic variants, such as Omicron. Antibody titers against both RBDs were lower in participants with chronic diseases and in multiparous.

Conclusions

This is the first report of simultaneous detection of antibody titers, against the Wuhan-Hu-1 RBD and OmicronBA.5 RBD, in breast milk from puerperal women vaccinated with 3 doses a COVID-19 protein subunit vaccine. There is a tendency to decrease the antibody response after vaccination, due to chronic diseases and multiparity.