Story highlights Continued immunizations, especially for people at highest risk because of age, exposure or health status, will be crucial to limiting the severity of outbreaks, if not their frequency, experts believe Early in the pandemic, when vaccines for the coronavirus were still just a glimmer on the horizon, the term âherd immunityâ came to signify the endgame: the point when enough Americans would be protected from the virus so we could be rid of the pathogen and reclaim our lives. Now, more than half of adults in the United States have been inoculated with at least one dose of a vaccine. But daily vaccination rates are slipping, and there is widespread consensus among scientists and public health experts that the herd immunity threshold is not attainable â at least not in the foreseeable future, and perhaps not ever.