Japan's Astellas Pharma Inc and San Diego-based Vical Inc said their experimental herpes vaccine failed a mid-stage study involving certain kidney transplant patients.
Vical's shares was down about 18 percent in light premarket trading on Monday.
The DNA vaccine, ASP0113, is designed to prevent cytomegalovirus (CMV) disease in patients receiving a renal transplant from a donor whose blood indicates a high likelihood of the presence of CMV.
CMV is a herpes virus that infects more than half of all adults in the United States by the age of 50, and is even more widespread in developing countries, the companies said on Monday.
The trial enrolled 150 kidney transplant recipients across 80 centers in North America, Europe and Australia, in which patients either received the vaccine or a placebo.
Once CMV enters a person's body, it stays there for life and can reactivate. Most infected people show no signs or symptoms because their immune system usually controls the virus.
However, the infection can pose serious problems for people with weakened immune systems, including HIV patients, organ transplant patients and babies infected with the virus before their birth.
Transplant recipients are particularly at risk because they take medicines that suppress their immune system. The infection is considered almost ubiquitous in renal transplant patients.
The vaccine, initially developed by Vical, is also being tested in a late-stage study in patients receiving a stem cell transplant. The results are expected late in 2017.
Cambridge, Massachusetts-based VBI Vaccines is also testing a CMV vaccine in an early-stage study.
(Reporting by Natalie Grover in Bengaluru; Editing by Ted Kerr and Savio D'Souza)