By Neil Murthy
Health officials are turning to strategies learned during the Ebola pandemic to combat the burgeoning Zika virus epidemic.
Dr. Ana Maria Henao-Restrepo, a medical epidemiologist from the World Health Organization, described her experience testing an experimental Ebola vaccine during the outbreak in Guinea in 2015. A Zika vaccine is still in the “early stages of development” and “could take a few years” according to the World Health Organization. But Henao-Restrepo’s Ebola vaccine trial could offer valuable lessons to tackle Zika.
In the Guinea outbreak, Henao-Restrepo and her team first had to identify a “ring of contacts” for a patient with Ebola. Anyone who came in close contact with a patient would be included in this ring. Using the process of “cluster randomization,” Henao-Restrepo and her colleagues administered the experimental vaccine to a random sample of close contacts. For another group, they waited 21 days after contact to administer the vaccine.
Henao-Restrepo then compared the two groups to see if study participants from either group would develop Ebola. Ten days after administering the vaccine, none of the contacts who immediately received it developed Ebola. There were cases of Ebola in the group who waited 21 days to receive the vaccine.
The results of her vaccine trial point to the efficacy of the intervention, and show how the experimental vaccine protected the contacts who immediately received it.
“It was an example of multilateralism,” said Henao-Restrepo. “We had to put together our best expertise and collaborated with partners in a close way. Nearly 400 people participated to make the trial happen.”
Now, some are considering whether it is possible to use a similar strategy to tackle Zika virus once the vaccine is available.
“I believe that for testing a Zika vaccine you can use a similar ring vaccination trial,” said Dr. Ira Longini, co-director of the Center for Statistics and Quantitative Infectious Diseases at the Emerging Pathogens Institute, University of Florida. Longini worked with Henao-Restrepo on the Ebola vaccination trial in Guinea.
Although Zika does not spread in the same way as Ebola and is mainly spread through mosquitoes, Longine argued that cases of Zika also appear in clusters, with a mosquito biting and infecting individuals staying in close contact. Therefore, when a Zika virus vaccine is eventually developed, the vaccine can be tested in a similar way as the experimental Ebola vaccine in Guinea.
“Certainly this is a possibility that could be explored,” said Geoffrey Siwo, a computational biologist at IBM Research – Africa. He attended the panel and presentations by Longini and Henao-Restrepo. Siwo said that there is still a lot to learn about the Zika virus before we can draw parallels between Ebola and Zika.
“As more data becomes available, we will know what study design will be best,” said Siwo.