Marcos López Hoyos
Scientific Director of the Valdecilla Health Research Institute (IDIVAL) and Professor of Immunology at the University of Cantabria
This is the analysis of the Danish registry, which is well collected with mRNA vaccinations (Pfizer and Moderna) and shows good vaccine protection against infection with the alpha and delta variants, dropping significantly with the omicron.
A strength of the study in Denmark was the high access to testing for covid-19 since the beginning of the pandemic. This is in line with other registries and papers.
Protection against hospitalisation from delta and omicron was very high.
It is a study that confirms everything described to date in other series and registries. As the authors say, the major limitation of the study is the non-randomisation of the groups, since at certain ages the vaccination rate was almost 100% and the unvaccinated reference group was not comparable.
They also include the effect of comorbidities as covariates, although they only use the sum of one to four comorbidities considered, without differentiating the differential effect.