Humoral Response After 5 Successive Doses of COVID-19 Vaccine in Kidney Transplant Patients: Comment.

Thank you for your share in relation to our publication “Humoral Response After Five Successive Doses of SARS-CoV-2 mRNA Vaccine in Kidney Transplant Patients.”1 Your contribution to the need to identify the asymptomatic patients who could have been infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) between booster vaccine doses is of great interest to us. The inclusion of these patients in our work could have led us to confuse the cause of the development of the humoral response, which may not be caused by the response to successive doses of booster vaccines but rather by the infection. To avoid this confounding factor, we determined the presence of SARS-CoV-2 IgG antibodies against the nucleocapsid (IgG anti-N) in all the patients of the study, and we excluded the positive ones. As it is well known, SARS IgG anti-N only becomes positive in patients infected by the virus and have passed the infection. Several articles have published the long-term persistence of SARS-CoV-2 IgG antibodies, which can be detected in up to 15 mo.2,3 Also, Perez-Saez et al demonstrated that SARS-CoV-2 IgG anti-N antibodies persisted for at least 8 mo in a cohort of mostly mildly symptomatic and asymptomatic infections.4 In addition, kidney transplantation patients usually have symptoms during infection. All of this information gives us enough data to reasonably state, with considerable certainty, that the patients included in our study did not experience any disease.