text: Hesitancy Toward a COVID 19 Vaccine The scientific community has come together in a mass mobilization to combat the public health risks of COVID 19 including efforts to develop a vaccine However the success of any vaccine depends on the share of the population that gets vaccinated We designed a survey experiment in which a nationally representative sample of 3 133 adults in the USA stated their intentions to vaccinate themselves and their children for COVID 19 The factors that we varied across treatments were the stated severity and infectiousness of COVID 19 and the stated source of the risk information White House or the Centers for Disease Control We find that 20 of people in the USA intend to decline the vaccine We find no statistically significant effect on vaccine intentions from the severity of COVID 19 In contrast we find that the degree of infectiousness of the coronavirus influences vaccine intentions and that inconsistent risk messages from public health experts and elected officials may reduce vaccine uptake However the most important determinants of COVID 19 vaccine hesitancy seem to be distrust of the vaccine safety including uncertainty due to vaccine novelty as well as general vaccine avoidance as implied by not having had a flu shot in the last two years 