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About a dozen COVID-19 vaccines have been approved around the world, providing a possible path out of the pandemic. But hurdles have emerged, including logistical issues around vaccine rollouts, a rising tide of worrisome variants, and uncertainty around the longevity of immunity. New trials underway to test combinations of different manufacturers’ vaccines seek to overcome some of these challenges.
“It’s really exciting that we have these combination trials,” says Sarah Caddy, a viral immunologist at the University of Cambridge. “If we can use different vaccines, that opens opportunities for vaccinating more people.” In addition, she notes, “there’s some evidence that mixing and matching vaccines could give us better immune responses.”
Vaccines induce immunity by training the immune system to recognize a piece of SARS-CoV-2 called an antigen—usually the spike protein, which the coronavirus uses to unlock human cells. Most currently authorized COVID-19 vaccines deliver this training ...
