A trial to test the safety of, and immune response prompted by, the latest candidate for a vaccine to protect against Zika virus infection has begun with injections among the first of what is planned to be 28 adult participants. Of the participants, 20 will receive an injection of a live, weakened non-replicating Zika virus created from the combined genetic material of different viral strains, and eight will receive a placebo.
If it is found safe, the vaccine candidate could be added to an vaccine candidate currently being tested for potential effectiveness against four types of dengue, to create a single vaccine against both diseases. Both candidates were developed by scientists at the National Institute of Allergy and Infectious Diseases, led by microbiologist Stephen Whitehead. Zika, transmitted by the Aedes aegypti mosquito that also spreads the dengue virus, has been transmitted locally in countries where dengue also is endemic, across Asia, Africa, Pacific islands, the Caribbean, and the Americas, including the United States.
While dengue fever can cause pain so debilitating it also is known as “breakbone fever,” and can cause death in as much as 20 percent of severe and untreated cases, the effects of Zika infection are more insidious, with immediate impacts often going unnoticed, or with mild symptoms of rash and fever. The more severe impacts of Zika virus infection, however, are devastating, including grave neurological birth defects among the infants of women infected with the virus while pregnant, and the paralyzing and potentially deadly Guillain-Barré syndrome among older individuals or those with weakened immune systems. In addition, the virus has been transmitted through semen, adding to the precautions that must be taken to avoid infection, and leading health officials not only to warn women who are pregnant to avoid travel to areas where the virus is being transmitted, but also to warn men traveling to those areas to avoid sex, or use condoms, for at least three months. As of last month the US Zika Pregnancy and Infant Registry had recorded 2474 pregnancies among women exposed to Zika across the United States and Washington, DC, and 4,900 in U.S. territories, including Puerto Rico and freely associated states, nine across the U.S. and 21 in U.S. territories in July alone. Research following Zika-exposed infants has found that disabling impacts of the virus can continue to emerge at least over the first year following birth.
No Zika vaccine candidate has been tested on pregnant women. Participants in the current trial, which will be conducted at the Johns Hopkins Bloomberg School of Public Health Center for Immunization Research in Baltimore, Maryland, and at the Vaccine Testing Center at the Larner College of Medicine at the University of Vermont in Burlington, will be healthy, not pregnant, not previously exposed to Zika, and between the ages of 18 and 50. All will record their temperatures on a regular basis and return for tests over the year that follows.
The trial is the second Zika vaccine trial sponsored by NIAID, which also supported the development of a vaccine candidate created from inactivated virus at the Walter Reed Institute of Research, and of a development through a United Kingdom based company of vaccine candidate against multiple mosquito-borne diseases.