U.S. health authorities on Wednesday authorized the use of synthetic antibodies developed by AstraZeneca to prevent COVID-19 infections in people who react badly to vaccines. It was the first time the Food and Drug Administration has given emergency authorization for such a purely preventative treatment. The FDA warned the drug Evusheld is “not a substitute for vaccination in individuals for whom COVID-19 vaccination is recommended” and can only be authorized for people with weakened immune systems or those who cannot be vaccinated for medical reasons, such a strong allergic reaction. In those cases, the drug can be administered to people 12 and older. Evusheld combines two types of synthetic antibodies (tixagevimab and cilgavimab), and is given as two intramuscular injections, one right after the other. These antibodies help the immune system fight off the virus by targeting its spike protein, which allows it to enter cells and infect them. The …