Zika virus infection is caused by one virus serotype, according to a study conducted by investigators from the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health, Emory University, and Washington University in St. Louis. The finding means that vaccination against a single strain of Zika virus should be sufficient to protect against genetically diverse strains of the virus.

The study is published in the journal Cell Reports.

"It’s very important to know that infection with Zika virus can produce antibodies that could fight any strain of the virus," says Mark J. Mulligan, MD, distinguished professor of medicine (infectious diseases) at Emory University School of Medicine, executive director of the Hope Clinic of the Emory Vaccine Center and co-author for the study report. "This result is encouraging and helpful in understanding the immune response to the virus and developing an effective Zika vaccine."

The closely-related Dengue virus has four serotypes, which is why people can be infected with dengue as many as four times, once with each serotype.

Zika virus strains are grouped into two distinct genetic lineages: African and Asian. The Zika virus strain circulating in the current outbreak in Central and South America and the Caribbean is of the Asian lineage.

When individuals are infected with Zika virus, their immune systems produce neutralizing antibodies to fight the infection. These antibodies may offer immunity against future infections by strains of the same Zika virus lineage. Until now, it was unclear whether the antibodies could also protect against infection with strains of the other Zika virus lineage. Results from laboratory experiments and tests in mice now show this may be possible. Such protection indicates that, despite being genetically distinct, all strains of Zika virus have identical surface antigens and therefore are the same serotype.

In this study, scientists took serum samples from people infected by Zika virus strains circulating in South America and mixed them with multiple strains of the virus in the laboratory to see how well the serum antibodies neutralized the virus. Results showed that antibodies elicited after infection with Zika virus strains of the Asian lineage were able to potently inhibit both Asian lineage and African lineage strains. The researchers conducted similar experiments using serum samples from mice and found that sera from mice infected with either Asian or African Zika virus strains were equally effective in neutralizing virus strains from either lineage.

The study results are important to the ongoing effort to rapidly develop a Zika vaccine. Because there is only one Zika virus serotype, antibodies elicited by any Zika virus strain in a vaccine could conceivably provide protection against all Zika virus strains, say the authors.

Reference:  KA Dowd et al. Broadly neutralizing activity of Zika virus-immune sera identifies a single viral serotype. CellReports DOI: 10.1016/j.celrep.2016.07.049 (2016).

The Hope Clinic of the Emory Vaccine Center is conducting an open NIH-funded study of the natural history, immunology and virology of Zika infections in returned travelers, currently enrolling participants with suspected or confirmed Zika virus infection. For more information, call 404-712-1371. A recent Emory press release also provides more information about that study: "Emory researchers join NIH study of individuals infected with Zika virus"