Saint Louis University’s Center for Vaccine Development is studying an investigational vaccine for yellow fever, a potentially deadly disease that is spread by the same mosquito that transmits Zika virus. The research is funded by the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.

Sarah George, M.D., is a Saint Louis University flavivirus expert who is studying a vaccine for yellow fever. Image/Saint Louis University
Sarah George, M.D., is a Saint Louis University flavivirus expert who is studying a vaccine for yellow fever.
Image/Saint Louis University

Yellow fever is among a family of flaviviruses that include Zika, dengue, West Nile virus and Japanese encephalitis, which are spread by Aedes mosquitoes. Concerned about the outbreak of yellow fever in Angola and its potential spread, a World Health Organization panel recently called yellow fever a serious public health event that required enhanced international support.

A new vaccine for yellow fever is needed because the current vaccine is not recommended for those who are most vulnerable and because Aedes mosquitoes are spreading rapidly, according to Sarah George, M.D., associate professor of infectious diseases at SLU and principal investigator for the clinical trial.

Those who have immune systems that are challenged — infants younger than 9 months, pregnant women, adults older than 60 and people who have cancer and other diseases that weaken the body’s immune system — are at increased risk of complications if they receive the current yellow fever vaccine.

While it is highly effective, the current yellow fever vaccine is attenuated, meaning it is made from a weakened strain of the live virus that can’t cause yellow fever. It can, however, cause health complications for those who have compromised immune systems. About 600 million doses of the current vaccine have been given, providing immunity to yellow fever for at least 10 years, George said.

“Because of how the existing vaccine is made, it is not recommended for certain groups of people. We need a safer vaccine that’s just as effective,” George said.

“If you’re a 65 year old retiree who wants to go on an African safari, you have a difficult decision to make. Getting the current vaccine has the risk of complication, yet you need to be protected against yellow fever, which can cause serious illness and even death,” George said.

George will study whether a new type of vaccine, which uses a modified smallpox vaccine as a vector to deliver yellow fever proteins to cells, stimulates the body’s defense system to protect against yellow fever. Her study will test the safety of the vaccine as well as immune responses of groups of volunteers who are given the investigational vaccine, the smallpox vaccine and the current yellow fever vaccine. Researchers also will investigate the impact of adding an adjuvant, which is an agent that enhances the body’s immune response, to the investigational yellow fever vaccine.

The phase 1 clinical trial is the first human study of the investigational vaccine for yellow fever. It is being conducted at SLU and the University of Iowa, which are among the National Institute of Allergy and Infectious Disease’s network of Vaccine and Treatment Evaluation Units (VTEUs). Researchers are recruiting about 90 healthy men and women between 18 and 45 years of age for the study, which will last eight months.

Endemic in Africa and South America, yellow fever annually infects about 200,000 people, causing symptoms that include fever, back pain, headache, nausea, vomiting, fatigue and weakness.

Most people recover but about 15 percent of those infected become severely ill with jaundice, bleeding and shock. Of those who develop severe disease, between 20 and 50 percent are at risk of death, with as many as 60,000 people dying each year.

“Yellow fever is a nasty disease and can kill you,” George said. “It’s truly miserable, and we need a vaccine that can protect more people.”