LONDON (Reuters) - U.S. infectious disease expert Anthony Fauci said on Sunday it would be clear whether a COVID-19 vaccine was safe and effective by early December, but that more widespread vaccination would not be likely until later in 2021. “We will know whether a vaccine is safe and effective by the end of November, the beginning of December,” Fauci told the BBC. “When you talk about vaccinating a substantial proportion of the population, so that you can have a significant impact on the dynamics of the outbreak, that very likely will not be until the second or third quarter of the year.”