In the United States, the Centers for Disease Control and Prevention is tracking nine cases in seven states, not all of which have a history of travel to countries where monkeypox is endemic. The monkeypox outbreak has grown to include about 260 confirmed cases and scores more under investigation in 21 countries. “We can’t guarantee that a person who was vaccinated against smallpox is still going to be protected against monkeypox,” Fauci said. “Even if they were vaccinated 50 years ago, that protection should still be there,” he said. Luigi Ferrucci, scientific director of the National Institute on Aging. “The bottom line is that even those that were vaccinated many decades before maintain a very, very high level of antibodies and the ability to neutralize the virus,” said Dr. Vaccinated older adults might become infected but are likely to escape with only mild symptoms.