As the number of cases of MERS, the Middle Eastern coronavirus, reaches 40 — with 20 deaths so far — the disease is behaving more and more like its relation, SARS, that killed nearly 800 people worldwide in 2003. However, MERS is not SARS — it binds to a different cell receptor, so the binding site is slightly different. The binding site “is an excellent candidate for vaccine development,” says UTMB’s Chien-Te Tseng, who collaborated on a study of SARS vaccines. But careful testing will be needed to ensure it really doesn't induce a harmful immune reaction, he says.