Experts answer questions with Johnson & Johnson vaccine on hold Medical experts say people who have already received the single-dose Johnson & Johnson vaccine should not panic. MILWAUKEE - The Wisconsin Department of Health Services (DHS) instructed vaccine providers on Tuesday, April 13 to stop administering the Johnson & Johnson COVID-19 vaccine due to a federal review of adverse side effects reported. The Centers for Disease Control and Prevention (CDC) and U.S. Food and Drug Administration (FDA) issued a statement saying six cases of a rare and severe type of blood clot have been reported in the U.S. out of 6.8 million Johnson & Johnson vaccine doses given.