Explained: How to predict success of vaccine without a big trial

Vaccines can trigger diverse immune responses, including the manufacture of antibody molecules that bind and block infectious viruses, and the activation of T cells that kill virus-infected cells.

Moderna’s vaccine provides protection against Covid-19 by triggering the production of antibodies against a key viral protein, a study in monkeys suggests. The insight — if confirmed in humans — could speed the development of next-generation vaccines.

Vaccines can trigger diverse immune responses, including the manufacture of antibody molecules that bind and block infectious viruses, and the activation of T cells that kill virus-infected cells.

By identifying the immune responses that can predict a vaccine’s success, scientists could more easily judge candidate vaccines, a Covid-19 research update published on Tuesday by the scientific journal Nature said. The update is part of a series of Nature’s summaries of key papers as they appear.

To identify which immune responses are important for Moderna’s vaccine, Barney Graham and Robert Seder at the US National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, and their colleagues gave monkeys a range of vaccine doses and exposed the animals to SARS-CoV-2 (‘Immune Correlates of Protection by mRNA-1273 Immunization against SARS-CoV-2 Infection in Nonhuman Primates’, K S Corbett et al. Preprint at bioRxiv https://doi.org/f8pf; 2021).

The vaccinated animals that had the lowest levels of viral genetic material in their noses and lungs also had the highest levels of antibodies that recognise the viral spike protein, the molecule that the Moderna vaccine encodes. Levels of other immune markers did not correlate as strongly with the vaccine’s protective effects.

In a one-sentence summary of their findings, the researchers said “mRNA-1273 vaccine-induced antibody responses are a mechanistic correlate of protection against SARS-CoV-2 infection in NHP”. MRNA-1273 is the technical name for the vaccine developed by Moderna. NHP stands for ‘non-human primates’, i.e. monkeys. The findings have not yet been peer reviewed.

A parallel study now under way will compare immune markers in people who were protected by jabs, including the Moderna one, with markers in people who were infected despite receiving a vaccine. Identifying these ‘correlates of protection’ will help researchers to assess existing and future vaccines without running costly, large-scale clinical trials.

News updates from Nature

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