An experimental COVID-19 vaccine that uses an atypical ingredient to stimulate an immune response shows promise against several variants of the coronavirus — at least in monkeys.

The mRNA COVID-19 vaccines stimulate the immune system by exposing it to the SARS-CoV-2 protein, called spike, that enables the virus to latch on to cells. David Veesler and Neil King at the University of Washington in Seattle and their colleagues made a vaccine that relies instead on a spike fragment called the receptor binding domain (RBD). They injected monkeys with nanometre-scale particles studded with dozens of RBDs and found that the vaccine generated virus-blocking ‘neutralizing’ antibodies against the Alpha, Beta and Gamma variants, and related animal coronaviruses. This vaccine is currently in phase III clinical trials.

The team also tested nanoparticle vaccines containing RBDs from a mix of sarbecoviruses, a family of coronaviruses that includes SARS-CoV-2. In mice, these vaccines triggered production of neutralizing antibodies against multiple coronaviruses.

These findings pave the way for a pan-sarbecovirus vaccine that could protect against SARS-CoV-2 variants and sarbecoviruses that jump from animals to humans in the future.