Illustration of the US physician and immunologist Drew Weissman (born 1959). Weissman and his colleague Katalin Karikoa at the University of Pennsylvania, Philadelphia, received the 2023 Nobel Prize in Physiology or Medicine for their work on mRNA (messenger ribonucleic acid) vaccines, which led to the successful development of the Covid-19 vaccine. They had been working separately on mRNA therapeutics, but had discovered that the mRNA would produce adverse immune reactions in the body. Together they worked on modifying the building blocks of the mRNA molecule so that it was able to avoid detection and destruction by the immune system. It was this non-immunogenic nucleoside-modified RNA that was used to make the Covid-19 vaccine.