Role of the 1st booster dose of COVID-19 vaccine in the protection against the infection: A fundamental public health tool

Introduction. The COVID-19 pandemic is having a huge impact on human health with high morbidity and mortality rates worldwide. Healthcare Workers (HCWs) are one of the most at risk categories to contract the infection. Effective anti-COVID-19 vaccines were approved in a very short time. Making the 1st booster dose is essential to induce a good protection against the infection. Methods. We conducted a retrospective sero-epidemiological survey of already existing data concerning the antibody response of a HCWs sample vaccinated with the primary cycle and the 1st booster dose of the Pfizer-BioNTech COVID-19 mRNA vaccine and, specifically, after three weeks from the third dose of vaccination. Results. In our analysis, after the primary cycle, a 95.15% effi‑cacy was detected. Among the non-responders, women were significantly more frequent (69.56%). Moreover, we found a significant reverse correlation between the immune response and the age of the sample, especially in women. However, the 1st booster dose completely cancelled these differences. Conclusions. Our data are perfectly in line with what has been declared by the conducted studies in terms of efficacy. However, it is important to highlight that people with only the primary cycle are at high risk to contract the COVID-19 infection. Therefore, it is necessary to not consider people vaccinated with the primary cycle completely risk-free and to stress the importance to perform the 1st booster dose.