An infectious disease expert from Johns Hopkins Bloomberg School of Public Health presented new results from the world’s first “controlled human infection” study with Zika virus at the annual meeting of the American Society of Tropical Medicine and Hygiene.
It showed two strains of the virus can be safely and effectively used to deliberately infect human volunteers, a major advance for Zika vaccine development — and for understanding more about the disease. Infections with the mosquito-borne virus — which experts fear may be ripe for sparking new epidemics — are typically mild or asymptomatic. But vaccines are needed to prevent infections during pregnancy that, during the 2016 outbreak in the Americas, were linked to severe birth defects and disabilities among fetuses and newborns.
Zika transmission in the hotspots of the 2016 outbreak is very low at the moment. But there are concerns the disease can re-emerge more intensely on roughly 10-year cycles, meaning a new outbreak could occur in just a few years, said Anna Durbin, MD, an expert in vaccines for mosquito-borne diseases at the Bloomberg School who led the Zika controlled infection study. She said the lack of current cases means the only way to test the effectiveness of vaccines in advance of an outbreak is by developing a way to safely infect or “challenge” human volunteers with the disease. That’s been controversial given the lack of a specific anti-viral drug for treating Zika. Durbin said her study was preceded by an extensive review by the U.S. National Institutes of Health (NIH), the U.S. Food and Drug Administration (FDA), and the World Health Organization (WHO), which found for Zika, what’s technically known as a “controlled human infection model,” or CHIM, offered a safe and useful pathway for vaccine development.
She said the study evaluated two strains of the virus in female volunteers who were neither pregnant nor lactating. They agreed to be admitted as patients at a Johns Hopkins Center for Immunization Research inpatient unit in Baltimore until they were completely free of the virus and to continue using highly effective birth control methods for two months. She said the 20 women who received the test strains — eight others got a placebo — all developed laboratory-confirmed infections, but with only mild illness. She said several vaccine manufacturers have inquired about using the strains to test Zika vaccine candidates. Durbin said there are now plans to evaluate controlled Zika infections in male volunteers, who also will remain on the inpatient unit until free of infectious virus, in part to assess how long Zika remains infectious in semen.
