A single immunization near birth elicits immediate and lifelong protective immunity.

Most existing vaccines do not induce protective immunity immediately following birth, nor do they retain protective efficacy in the latter years of life without booster doses. Using a mouse model, we present evidence that a live-replicating vaccine administered only once shortly after birth was able to induce both immediate and lifelong protection. Newborn mice immunized with a safe, highly attenuated strain of Listeria monocytogenes (Lm) were already protected by day 7 post-vaccination when challenged with a virulent strain of Lm. Furthermore, all mice remained fully protected for 2 years after only a single immunization. Vaccine-specific T cell immune responses were still detectable 2 years later, indicating long-lived immune memory even in neonatal vaccine recipients. Analysis of memory precursor subsets, specific for antigens homologous to Lm or a model vaccine (Ova), demonstrated remarkable similarity between adult and neonatal vaccine recipient effector and central memory CD8 T cell development. The magnitude of expansion of antigen specific memory T cells post-infectious challenge correlated with protection in both groups. This is the first direct evidence that vaccination--even in the absence of a booster dose--is capable of inducing immediate and lifelong protective immune memory regardless of age at the time of initial vaccination.