Three Vaccine Doses (IMAGE) Johns Hopkins Medicine Caption Johns Hopkins Medicine researchers have shown that three doses of vaccine against SARS-CoV-2 -- the virus that causes COVID-19 -- increase antibody levels more than the standard two-dose regimen for people who have received solid organ transplants. The researchers say this finding suggests booster doses should be investigated for those who are immunocompromised. Credit Graphic created by M.E. Newman, Johns Hopkins Medicine, with public domain images and background artist rendition of SARS-CoV-2 courtesy of the U.S. Centers for Disease Control and Prevention Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.