Herd immunity against the virus that causes COVID-19 may be impossible to reach, a federal health official said in little-noticed remarks earlier this month. “We would discourage a strict goal of a threshold where we think if we reach that, that community transmission will then cease,” Dr. Jefferson Jones, a medical officer on the Centers for Disease Control and Prevention’s (CDC) COVID-19 Epidemiology Task Force told a panel of the agency’s vaccine advisers. “I think thinking that we will be able to achieve some kind of threshold where there’ll be no more transmission of infections may not be possible,” Jones said. Herd immunity, or community immunity, refers to a situation where a certain percentage of a population has immunity against an infectious disease. Immunity can come from vaccination or prior illness. When the percentage is reached, the collective immunity offers some protection to people without immunity because “the disease has little …