Researchers infect women with Zika virus to help find a vaccine
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Key takeaways:
- Researchers identified two Zika virus strains that could safely be used to infect people in a vaccine trial.
- Manufacturers have already inquired about using them to test vaccine candidates.
Researchers completed the first ever human challenge trial for Zika virus, deliberately infecting volunteers to identify strains of the virus that can be safely used to test vaccines against the mosquito-borne pathogen.
Details of the study were presented at the annual meeting of the American Society of Tropical Medicine & Hygiene. The study enrolled only women, but researchers have also began evaluating controlled infections in men, according to Anna Durbin, MD, director of the center for immunization research at the Johns Hopkins Bloomberg School of Public Health.
The trial is part of an effort to develop a vaccine against Zika virus, which will be especially important to protect pregnant people, Durbin told Healio.
In 2016, WHO declared a global public health emergency over Zika in response to an epidemic of the virus that started in 2015 in Brazil and spread throughout the Americas. Brazil experienced the largest number of cases during the epidemic — more than 300,000. There were more than 41,000 cases of confirmed or probable Zika virus infections in the United States in 2016, according to the CDC, with most of them occurring in U.S. territories.
Although people infected with Zika virus experienced mostly mild symptoms, babies born to mothers infected with the virus face an increased risk for a suite of severe birth defects and disabilities, including severe microcephaly.
Zika vaccine research continues, but because there is no ongoing outbreak, researchers are not able to test vaccine candidates in phase 3 field trials. The lack of cases means the only way to test vaccines is to develop safe human challenge trials.
Durbin and colleagues completed the first one earlier this year using isolates obtained from people who had uncomplicated Zika virus infection — they were only mildly symptomatic, Durbin explained — to identify two viral strains that could potentially be used for human challenge studies.
They recruited 28 women to participate in the study, admitting them to the Johns Hopkins Center for Immunization Research inpatient unit and assigning them to one of two cohorts. In each cohort, 10 women were infected with the virus strains and 4 received a placebo.
All participants receiving the viral strains developed lab-confirmed Zika infections, with mild illness, and were hospitalized until they were completely free of the virus. The participants continued to use birth control for 2 months.
The trial demonstrated that both test strains are “highly infectious and have an acceptable safety and virologic profile,” Durbin and colleagues said. Several vaccine manufacturers have already inquired about using the strains to test vaccine candidates, according to Durbin.
“If a vaccine demonstrates efficacy, it would still need to be evaluated in a few thousand volunteers for safety — in a field study, not a challenge study. If it gets provisional licensure based on this, effectiveness would need to be demonstrated in a post-licensure study,” Durbin said.
She said they have already started a similar controlled Zika infection study in male volunteers who will remain as inpatients until they clear the virus, specifically to assess how long it remains infectious in semen.
References:
- CDC. Zika virus: Zika cases in the United States. https://www.cdc.gov/zika/reporting/index.html. Last reviewed Oct. 11, 2023. Accessed Oct. 25, 2023.
- Choy RKM, et al. Clin Microbiol Rev. 2022;doi:10.1128/cmr.00008-21.
- Durbin AP, et al. Development of a controlled Zika human infection model. Presented at American Society of Tropical Medicine & Hygiene; Oct. 18-22; Chicago.
- Zhong D, et al. Open Forum Infect Dis. 2022;doi:10.1093/ofid/ofac492.1758.
Perspective
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I have been involved in following patients with Zika virus infection in pregnancy and their offspring for neurodevelopment for the past 7 years. The surviving children born during the 2015-2017 Zika virus epidemic are now 6 to 8 years of age. During this time, we have developed a greater understanding of the spectrum of neurodevelopmental impairments from antenatal Zika virus exposure in offspring, but we are yet to be able to prevent the infection that has such detrimental effects on pregnancy and the developing brain.
During the COVID-19 pandemic, many vaccine research efforts on Zika virus were shifted toward SARS-CoV-2, leaving us unprepared and without a vaccine for the likely eventual recurrence of a Zika virus epidemic. In addition, the current low levels of circulating Zika virus make it hard to test vaccine safety and effectiveness.
Knowing that the illness caused by Zika virus in low-risk nonpregnant adults is generally mild, developing a controlled human infection model can enable necessary studies to develop an effective vaccination. Human research volunteers infected by Zika virus have the potential to lead to lifesaving vaccines for Zika virus to prevent serious disability and death from this congenital infection in future generations from future Zika virus epidemics.
As a society, we need to invest in developing safe and effective vaccines for mosquito-borne diseases to hopefully prevent future viral epidemics. We know that viruses are not going away, and vaccination can be lifesaving. Preventing another Zika virus epidemic through vaccination would be an outstanding scientific and public health achievement.
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Durbin AP, et al. Development of a controlled Zika human infection model. Presented at American Society of Tropical Medicine & Hygiene; Oct. 18-22, 2023; Chicago.
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