A single-shot Lassa vaccine induces long-term immunity and protects cynomolgus monkeys against heterologous strains.

One Shot for Lassa Virus: Up to 180 million people are at risk for infection with Lassa virus (LASV), and the endemic region for LASV is expanding. Thus, there is a critical need to develop a vaccine against LASV, preferably one that protects against multiple lineages of LASV, generates durable immune responses, and can be administered in a single dose. To that end, Mateo et al. investigated the ability of a recombinant measles virus vaccine expressing LASV proteins (MeV-NP) to protect nonhuman primates against multiple strains of LASV and to provide protection over a year after vaccination, showing that the vaccine was effective at both. MeV-NP, which is now in clinical trials, represents an advance in the field of LASV vaccine development. A safe and protective Lassa virus vaccine is crucially needed in Western Africa to stem the recurrent outbreaks of Lassa virus infections in Nigeria and the emergence of Lassa virus in previously unaffected countries, such as Benin and Togo. Major challenges in developing a Lassa virus vaccine include the high diversity of circulating strains and their reemergence from 1 year to another. To address each of these challenges, we immunized cynomolgus monkeys with a measles virus vector expressing the Lassa virus glycoprotein and nucleoprotein of the prototypic Lassa virus strain Josiah (MeV-NP). To evaluate vaccine efficacy against heterologous strains of Lassa virus, we challenged the monkeys a month later with heterologous strains from lineage II or lineage VII, finding that the vaccine was protective against these strains. A second cohort of monkeys was challenged 1 year later with the homologous Josiah strain, finding that a single dose of MeV-NP was sufficient to protect all vaccinated monkeys. These studies demonstrate that MeV-NP can generate both long-lasting immune responses and responses that are able to protect against diverse strains of Lassa virus. [ABSTRACT FROM AUTHOR]