Limited data are available on immunoresponses to single- and/or double-dose vaccination, and vaccine responses following previous natural infection have not been assessed in clinical trials , , . t12 for infection-na?ve and subjects with previous-natural infection who present higher values of specific antibodies, while no significant differences have been found between t12 and t28. No statistically significant difference was found between male and female, while lower Ab levels have been observed in subjects older than 60?years at t12 but not at t28. Conclusions Our study confirms observed differences in vaccine responses between infection-na?ve and subjects with previous natural Dacarbazine infection at t12 but not for a longer time. The influence of sex and age deserves further studies, even if the relationship with age seems particularly significant. strong class=”kwd-title” Keywords: COVID-19, SARS-CoV-2 vaccine, BNT162b2, Antibody, Serology, Immunological response, Immunoassays 1.?Introduction Coronavirus disease 2019 (COVID-19) is a major public health issue. To contrast the spread of SARS-CoV-2, the rapid immune-induced vaccination has been suggested as a key global strategy and, currently, a total of 82 vaccines are in clinical development, and 182 are in pre-clinical development (https://www.who.int/publications/m/item/draft-landscape-of-covid-19-candidate-vaccines). Several of the vaccines currently developed are based on a double-dose, the primary and boost approach. This strategies allowed to obtain a high immunity, which was demonstrated, Rabbit polyclonal to NFKBIZ for example, to be effective in preventing 95% of Covid-19 cases for BNT162b2 (Pfizer/BioNTech, Comirnaty) . Similarly, strong evidence has been reported that a second dose enhances the antibody response in other vaccines , . In most European countries, the vaccination campaigns started between the 26 and 31 December 2020 after the first lots of Comirnaty vaccine were delivered . The vaccine generates an immune response against the S1 spike protein, the titers of which Ab correlate with functional viral neutralization , . Up to now, only few studies have provided pieces of evidence about the immunological status of infection-na?ve vaccinated subjects and previous natural infection. Interestingly, very elevated Ab titers were described by two recent studies from Manisty et al. and Prendecki et al, the latter further showing an inverse correlation with age of Ab levels. However, to better clarify immunological response to the two vaccinal inoculums, several time points should be inspected since it has been shown that at least 12C14?days are necessary to mount a valuable antibody response . Furthermore, subjects should be well characterized from their previous infection status. This latter point is particularly important for evaluate the necessity of implementing the boosting dose in previous natural-infection subjects, when Ab levels were already elevated. Since several immunoassay methods for measuring SARS-CoV-2 Ab were designed to detect N- or generic S-protein antigens, this caused a potential issue on Ab measurement, and methods should be validated for this purpose, or neutralization activity assay should be chosen as alternative. However, this latter technique needs handle live virus in BSL-3 laboratories and for this reason, a surrogate method to evaluate their levels in patients has been strongly advocated . In this study, a well-defined cohort of healthcare workers (HCW) was tested for serum SARS-CoV-2 Ab after 12 and 28?days after the first inoculum of BNT162b2 with two different chemiluminescent immunoassays. The cohort includes a series subjects who presented previous natural contamination during the first or second wave of pandemic. The aims of this study are to investigate the Ab levels in previous natural contamination and infection-na?ve subjects, and to assess further correlations with age and gender. 2.?Material and methods This study included a series of 163 HCW of the Padua University Hospitals, who underwent a complete vaccination campaign (primary dose followed by a boost dose after 21?days) Dacarbazine between December 26th 2020 and March 10th 2021. A total of 125 individuals included in this study were previously enrolled in a follow-up study, carried out between April 8 and May 29, 2020, Dacarbazine for determining SARS-CoV-2 serological levels as described elsewhere , while the other 38 included subjects were post-graduate medical trainees. All subjects underwent periodical nasopharyngeal swab testing (every 2 or 3 3?weeks) from March 2020 to.