The three U.S.-authorized vaccines provoke immune systems in similar ways. Each alerts immune fighters to SARS-CoV-2, the virus that causes covid-19, by exposing the body to the virus’s spike protein, said Dan H. Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston, whose laboratory helped develop the J&J shot. While it’s likely that adding a booster to any of the available vaccines will increase immune responses, “how that translates into clinical protection, that’s the part that’s not yet known,” Barouch said.
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