The delays in the production and delivery of COVID-19 vaccines and the growing number of fatal infections across the globe raised the question whether it would be more advantageous to vaccinate a larger group of individuals with one dose instead of a smaller one with two doses. Through a group of vaccinated healthcare workers, we describe the qualitative and quantitative serological response to a single dose of the BNT162b2 vaccine. We found that, before the second dose inoculation, 95.3 % (182/191) already had anti-SARS-CoV-2 IgG and, half of them, antibodies concentrations against RBD (the key target of neutralizing antibodies) that reached maximum values for the used evaluation immunoassay. In order to improve the execution of vaccination programs, further studies are needed to assess whether there are individuals for whom a single dose of mRNA vaccine or a delay in the inoculation of the second dose, produce a sufficient immune response. Additionally, follow-up studies will help in understanding post-vaccination immunity, how long it lasts and how it relates to infection and reinfection.