The findings, published in Science Immunology, suggest only a single vaccine dose may be needed to produce a sufficient antibody response. Researchers found that those who did not have COVID-19—called COVID naïve—did not have a full immune response until after receiving their second vaccine dose, reinforcing the importance of completing the two recommended doses for achieving strong levels of immunity. The study provides more insight on the underlying immunobiology of mRNA vaccines, which could help shape future vaccine strategies. “These results are encouraging for both short- and long-term vaccine efficacy, and this adds to our understanding of the mRNA vaccine immune response through the analysis of memory B cells,” says senior author E. John Wherry, chair of the department of systems pharmacology and translational therapeutics at the University of Pennsylvania and director of the Penn Institute of Immunology in the Perelman School of Medicine.