By LAURAN NEERGAARD
AP Medical Writer
Researchers report a third dose of Moderna’s COVID-19 vaccine substantially improved protection for organ transplant recipients. Their weak immune systems don’t always rev up enough with the standard two shots. Canadian researchers divided 120 transplant recipients, giving half a third dose and the rest a dummy shot two months after they finished standard vaccinations. It’s the most rigorous attempt yet to tell if a third dose in these vulnerable patients helps. The results were published Wednesday in the New England Journal of Medicine.