Different SARS-CoV-2 vaccines are approved in various countries, but few direct comparisons of the antibody responses they stimulate have been reported.

In thi paper the authors collected plasma specimens in July 2021 from 196 Mongolian participants fully vaccinated with one of four COVID-19 vaccines: Pfizer/BioNTech, AstraZeneca, Sputnik V and Sinopharm.

Functional antibody testing with a panel of nine SARS-CoV-2 viral variant receptor binding domain (RBD) proteins reveal marked differences in vaccine responses, with low antibody levels and RBD-ACE2 blocking activity stimulated by the Sinopharm and Sputnik V vaccines in comparison to the AstraZeneca or Pfizer/BioNTech vaccines.

RBD-ACE2 blocking antibody activity was strikingly different between the vaccines tested. Within each vaccine group, differences were also observed in antibody activity for the different viral variant antigens, although these were smaller than the differences between the vaccine groups.

The Pfizer/BioNTech vaccine elicited the strongest RBD-ACE2 blocking antibody activity, followed by AstraZeneca vaccine, then Sputnik V, with the lowest levels from Sinopharm.

Differences between the vaccine responses were highly significant for most viral variant antigens, although differences between the Sputnik V and AstraZeneca did not always reach significance.

RBD-ACE2 blocking antibody activity for RBD antigens of viral variants of concern or interest showed a consistent hierarchy of decreased blocking, with the greatest decrease for the Beta, Gamma and P.3 variants and more modest decreases for the other variants.

Anti-RBD and anti-spike binding assay data were similar to RBD-ACE2 blocking antibody results, with decreasing antibody concentrations from Pfizer/BioNTech to AstraZeneca to Sputnik V to Sinopharm.

The age of vaccine recipients and proportions of males and females in each group were comparable. RBD-ACE2 blocking antibody median values were lower for males than females to the Pfizer/BioNTech and Sinopharm vaccines, but not to the AstraZeneca and Sputnik V vaccines.

This direct comparison of vaccine-elicited functional antibody responses to a panel of nine SARS-CoV-2 viral variant RBDs indicates that there are marked differences in the serological responses generated by each vaccine, with relatively low antibody concentrations and RBDACE2 blocking activity stimulated by the Sinopharm and Sputnik V vaccines, intermediate levels for the AstraZeneca vaccine, and the highest values for the Pfizer/BioNTech vaccine.

The reasons for the differences in the serological responses between these vaccine types likely to include factors such as the antigen doses provided or expressed by the recipient’s cells, the anatomical distribution of antigen, adjuvant effects and the degree of stimulation of innate immune mechanisms, and the timing and nature of the priming
and boost vaccinations, among other possibilities.

The Authors conclude that these data indicate that there are major differences in the magnitude of functional
antibody responses stimulated by the four vaccines studied, and suggest that additional public health interventions such as booster vaccine doses, potentially with the more potent vaccine types, may be needed to further control the COVID-19 pandemic worldwide.

The Alpha variant caused 97% of infections in Mongolia in June and early July 2021. Individuals who recover from SARS-CoV-2 infection after vaccination achieve high antibody titers in most cases.

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