Federal officials expect their recommended pause on Johnson & Johnson COVID-19 vaccines will last "a matter of days," the head of the U.S. Food and Drug Administration said Tuesday. Acting FDA Commissioner Dr. Janet Woodcock said the exact time frame will depend on what officials learn over the next few days in their review of six cases of a severe blood clot reported after receiving the J&J shot, which she said seems to be "extremely rare." The FDA and the Centers for Disease Control and Prevention on Tuesday announced they were recommending a pause on delivering J&J vaccines while those reports of a combination of the blood clot and a low platelet count â from six women in the U.S. between the ages of 18 and 48, among a pool of more than 6.8 million J&J doses administered nationwide â are investigated. Subsequently, the Massachusetts Department of Health directed providers here to stop giving J&J vaccines while the review plays out.