Reacción a "Reactions to study claiming three doses of covid-19 vaccines protect better than two"

The study by Gram et al. clearly demonstrates that a third dose of vaccine is necessary to obtain durable protection against SARS-CoV-2. The main strength of the study is the large sample size, as it was conducted in the Danish population.

However, it does not add anything new to our knowledge. It has been quite clear for quite some time already from several previous studies that, while two doses provided good protection against the pre-omicron variants, this was not the case against omicron. Omicron is quite different from the original strain, which is the immunogen contained in the current vaccines, so three doses are necessary for the whole population, as omicron is the hegemonic variant at present. The most recent studies are already evaluating the effectiveness of four doses.