Science reports:

Individuals facing the threat of COVID-19 may care most about a vaccine’s ability to forestall grave disease that could lead to a hospital bed or worse. And a number of vaccines perform that vital task well, including those from Johnson & Johnson and AstraZeneca, which are based on genetically engineered cold viruses, as well as the not-yet-authorized protein vaccine from Novavax. But for public health experts trying to halt a global pandemic, shutting down even the mildest infections is also crucial, especially as the highly infectious Delta variant surges in scores of countries. By that measure, according to a brace of new studies, the messenger RNA (mRNA) vaccines from the Pfizer-BioNTech collaboration and Moderna stand out.

“All COVID-19 vaccines are not created equal,” says Eric Topol, a physician-scientist at the Scripps Research Translational Institute. “It’s clear that the two mRNA vaccines are highly effective at preventing infection—and that others wouldn’t be expected to break the chain as well.”

The large clinical trials that persuaded governments around the world to authorize COVID-19 vaccines mostly looked at their ability to block symptomatic disease and illness severe enough to lead to hospitalization or death. Preventing all infections, including those with no symptoms at all, is “rather a neglected endpoint,” says Adeel Butt, an epidemiologist and infectious disease specialist at the Veterans Affairs Pittsburgh Healthcare System. Yet, “It’s very, very important … to break the transmission of infection,” says Butt, who also works at Weill Cornell Medicine, Qatar.

Last week, Butt and his colleagues published some of the strongest evidence showing the mRNA vaccines can do just that. [Continue reading…]