Re: heterologous gam-COVID-vac (sputnik V)/mRNA-1273 (Moderna) vaccination.

To the Editor,

We would like to correspond on the publication, “Heterologous gam-covid-vac (sputnik V)/mRNA-1273 (Moderna) vaccination induces a stronger humoral response than homologous sputnik V in a real-world data analysis” [1]. When compared to the homologous SpV/SpV immunisation, Pereson et al. found that the heterologous SpV/Mod combination against SARS-CoV-2 is well tolerated and greatly boosts humoral immune response [1]. We concur that COVID-19 immunisation, in whatever form, can provide protection and has clinical benefits. In this sense, this study can provide some proof. However, it's important to remember that confounding factors can affect the immunological parameters being assessed. Infection with COVID-19 is common, and it can be re-infected without generating symptoms [2]. Following immunisation, there is a potential of asymptomatic COVID-19, which could make detecting immunological symptoms difficult. The possibility of asymptomatic COVID-19 must be ruled out.

Transparency declaration

The authors declare that they have no conflict of interest.

No external funding was received.

Author contributions

RM contributed 50% ideas, writing, analyzing, and final approval for submission. VW contributed 50% ideas, supervising, and final approval for submission.