Delaying second dose of Pfizer-BioNTech SARS-CoV-2 vaccine may be feasible in some cases Researchers in Spain have conducted the most extensive study to date investigating the effectiveness of vaccinating healthcare workers with a single dose of the Pfizer-BioNTech vaccine to protect against coronavirus disease 2019 (COVID-19). The team says one dose of the vaccine induced a much stronger antibody response against the causative agent – severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – among healthcare workers who had previously been infected with the virus than among those who had not. The researchers say that given the controversy over how to ensure adequate immunization of the population in times of vaccine shortages, the study findings might help inform decisions over whether to only administer a single dose in some cases.