At the American Association for the Advancement of Science meeting in Boston last weekend, Emory Vaccine Center researcher Mark Mulligan presented some limited findings on immune responses in Zika-infected humans, who were returned US travelers or expatriates.

The results were intriguing, despite the small number of study participants: five, two of whom were pregnant. Detailed information has not been available about immune responses against Zika in humans, especially T cell responses.

Highlights from Mulligan’s abstract:

*All five seemed to have a hole in their immune systems – functional antiviral “killer” CD8 T cells were rare, despite activation of CD8 T cells in general and strong responses from other cell types.

*Cross-reactive immune responses, based on previous exposure to dengue and/or yellow fever vaccine, may have blunted Zika’s peak.

*”Even with prolonged maternal viremia, both pregnancies resulted in live births of apparently healthy babies.”Zika infection during pregnancy can cause birth defects affecting the fetal brain. The infection is often reported to be asymptomatic or have relatively mild symptoms, such as a rash, lasting around a week. The longer infection periods in the pregnant women (more than 44 days in one case) bear some similarity to reports of an extended period of Zika infection in pregnant rhesus macaques.

The lack of antiviral CD8 T cells could be similar to the plentiful but inactive CD8 T cells seen during dengue infection, recently reported by Emory and New Delhi researchers.

Mulligan is executive director of the Hope Clinic of the Emory Vaccine Center. Emory’s news release on the beginning of this study is here. Some of the results were previously presented at the Emory Department of Medicine’s 2016 Research Day. Several Zika vaccines are in development, including one being tested at NIAID and Emory.