As Zika virus fears ramp up with the first U.S. cases of mosquito-borne transmission in Florida, researchers at the University of Maryland plan to begin testing a vaccine in humans before the end of the year.
The potential vaccine, which has shown promise in animal studies, is among the first to be in people as researchers race to curtail the virus blamed for a devastating birth defect that stunts brain development in newborns.
"A safe and effective vaccine to prevent Zika virus infection and the devastating birth defects it causes is a public health imperative," Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said in announcing that the University of Maryland School of Medicine's Center for Vaccine Development would be one of three study sites for the vaccine.
Other sites for the study, which will involve dozens of healthy volunteers, are Emory University in Atlanta and the National Institutes of Health Clinical Center in Bethesda.
"NIAID worked expeditiously to ready a vaccine candidate, and results in animal testing have been very encouraging," Fauci said in a statement. "We are pleased that we are now able to proceed with this initial study in people. Although it will take some time before a vaccine against Zika is commercially available, the launch of this study is an important step forward."
Researchers will look at the safety of the vaccine first and whether there is any immune response in this early test. If it's successful, other trials will be conducted in more affected countries.
One alternative vaccine, developed by Inovio Pharmaceuticals in Pennsylvania, has already been injected into its first human subject, that company announced last week. A vaccine based on a weakened version of the Zika virus, developed by Walter Reed Army Institute of Research in Silver Spring, is scheduled to begin human testing in October. That vaccine candidate showed promise in a recent study in monkeys, according to research published Thursday in the journal Science.
While Zika is a mild infection for most people, the virus is now known to cause microcephaly, which stunts the growth of babies' heads and brains. The virus is spread by certain mosquitoes and through sexual contact.
With cases mounting in South and Central America, the World Health Organization declared Zika a public health emergency in February.
The U.S. Centers for Disease Control and Prevention reports that there are more than 1,600 cases of Zika in the mainland United States, including 433 pregnant women. The agency has reported a small number of pregnancy complications and babies born with the disorder.
Maryland has reported 54 travel-related cases of Zika but is not separately reporting how many are pregnant women.
Until last week all of the U.S. cases were seen in people who had traveled to countries primarily in Latin America and the Caribbean or had sexually transmitted infections.
Florida public health officials reported July 29 that they had discovered four cases of Zika transmitted locally by mosquitoes, and have since updated that number to 15. That state's health officials have been monitoring and testing for more cases and have stepped up mosquito control in the region.
The CDC, which for months has said locally transmitted cases were expected, issued a rare warning for pregnant women and women who plan to become pregnant to stay away from the Miami area where the cases were found. The CDC has also warned pregnant women across the country to cover up and use insect repellent to avoid mosquito bites, and be tested for the virus.
There is no treatment for Zika, but medical providers have been using ultrasounds to identify and monitor for problems with the fetuses of pregnant women.
In Maryland, local and state health departments have distributed kits to pregnant women including repellent, condoms and larvicide, and advised residents to dump standing water where mosquitoes breed. State agriculture officials plan to continue their normal spraying for mosquitoes and target any area that reports a case of Zika.
But there's no greater preventative measure than a vaccine, which does not yet exist.
The Zika vaccine being tested at the University of Maryland represents a new avenue for preventing infection, one using the DNA code for the virus. It builds on another similar vaccine developed for West Nile virus, which has gone through rounds of testing but is not yet licensed for use.
NIH scientists engineered a small piece of DNA called a plasmid that contains genes that code for proteins in the Zika virus. Once the plasmid-based vaccine is injected into someone, the researchers believe their body will respond by creating antibodies and T cells that protect against the virus.
The DNA contains no infectious material and can't cause a Zika infection, said Dr. Monica McArthur, the principal investigator for the Maryland trial and an assistant professor in pediatrics in the school of medicine.
That's a big benefit to such a vaccine, she said. Traditional vaccines that use a live but weakened virus can't be given to people with compromised immune systems because they may cause infections.
McArthur said trial leaders will soon be recruiting volunteers, who are likely to come from the scientific community as well as the broader community. The volunteers will be followed over time.
Even if the trials are successful on this expedited schedule, a commercially available vaccine it could be a couple of years off. Typically vaccine development take 10 to 15 years.
The West Nile vaccine gave NIH scientists a significant boost in developing the Zika vaccine, McArthur said.
"Everyone is working together to get a vaccine as soon as possible, but we want to make sure it's a safe and effective vaccine," McArthur said. "We don't want to shortcut things."
Other government, academic medical institutions and pharmaceutical firms are investigating vaccines for Zika, including the Johns Hopkins University and an affiliated firm. They include other vaccines developed from DNA and from live weakened virus.
Pharos Biologicals LLC, formed last December by Hopkins researchers, is developing a DNA-based vaccine for Zika and also plans human trials soon, in addition to similar vaccine for other flaviviruses, a category that includes West Nile virus, dengue, tick-borne encephalitis virus and yellow fever.