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.

COVID-19 疫苗生产和交付的延误以及全球致命感染数量的不断增加引发了一个问题，即为较大群体的人接种一剂疫苗是否比为较小的群体接种两剂疫苗更有利。通过一组已接种疫苗的医护人员，我们描述了单剂 BNT162b2 疫苗的定性和定量血清学反应。我们发现，在第二剂接种之前，95.3% (182/191) 已经具有抗 SARS-CoV-2 IgG，其中一半的人针对 RBD（中和抗体的关键目标）的抗体浓度达到了最大值使用的评估免疫测定法。为了改善疫苗接种计划的执行，需要进一步研究来评估是否有个体接受单剂 mRNA 疫苗或延迟接种第二剂疫苗会产生足够的免疫反应。此外，后续研究将有助于了解疫苗接种后免疫力、其持续时间以及它与感染和再感染的关系。