COVID-19 mRNA Vaccines Preserve Immunogenicity after Re-Freezing.

The massive COVID-19 vaccine purchases made by high-income countries have resulted in important sample losses, mainly due to the complexity of their handling. Here, we evaluated the possibility of preserving the immunogenicity of COVID-19 mRNA vaccines after re-freezing vials, following the extraction of the maximum possible number of samples, as an alternative approach to minimizing their wastage. Thus, we exposed the vaccine vials to different re-freezing conditions and evaluated mRNA integrity and the effects in mice after in vivo administration. We reveal that the mRNA integrity of Comirnaty® and Spikevax® vaccines remained unaffected after re-freezing during 1 month at -20 °C or -80 °C. The immunological responses also remained unchanged in mice after these re-freezing conditions and no apparent side effects were revealed. The preservation of mRNA integrity and immunogenicity under these handling conditions opens the possibility of re-freezing the mRNA COVID-19 vaccine vials to limit their wastage and to facilitate vaccination processes.

The mRNA-1273 Vaccine Induces Cross-Variant Antibody Responses to SARS-CoV-2 With Distinct Profiles in Individuals With or Without Pre-Existing Immunity.

mRNA-based vaccines effectively induce protective neutralizing antibodies against SARS-CoV-2, the etiological agent of COVID-19. Yet, the kinetics and compositional patterns of vaccine-induced antibody responses to the original strain and emerging variants of concern remain largely unknown. Here we characterized serum antibody classes and subclasses targeting the spike receptor-binding domain of SARS-CoV-2 wild type and α, ß, γ and δ variants in a longitudinal cohort of SARS-CoV-2 naïve and COVID-19 recovered individuals receiving the mRNA-1273 vaccine. We found that mRNA-1273 vaccine recipients developed a SARS-CoV-2-specific antibody response with a subclass profile comparable to that induced by natural infection. Importantly, these antibody responses targeted both wild type SARS-CoV-2 as well as its α, ß, γ and δ variants. Following primary vaccination, individuals with pre-existing immunity showed higher induction of all antibodies but IgG3 compared to SARS-CoV-2-naïve subjects. Unlike naïve individuals, COVID-19 recovered subjects did not mount a recall antibody response upon the second vaccine dose. In these individuals, secondary immunization resulted in a slight reduction of IgG1 against the receptor-binding domain of ß and γ variants. Despite the lack of recall humoral response, vaccinees with pre-existing immunity still showed higher titers of IgG1 and IgA to all variants analyzed compared to fully vaccinated naïve individuals. Our findings indicate that mRNA-1273 vaccine triggered cross-variant antibody responses with distinct profiles in vaccinees with or without pre-existing immunity and suggest that individuals with prior history of SARS-CoV-2 infection may not benefit from the second mRNA vaccine dose with the current standard regimen.