There’s a new virus in town, and it doesn’t care who you are. The Delta variant of the mosquito-borne Zika virus is spreading through vaccinated households, according to a study by Brazilian researchers published Friday in the Journal of Infectious Diseases.
Researchers analyzed the blood of 15 family members living in a vaccinated household, and found that all but one had developed antibodies to Zika after contracting the virus. All of them reported having mild symptoms typical of the infection, including fever, skin rashes and swollen lymph nodes.
However, when they tested the occupants’ urine samples, genetic material from the virus was found in eight, meaning they had been carriers while symptomatic.
Zika is a relatively new disease, having first appeared in northeastern Brazil last year. The World Health Organization declared a global health emergency over concerns that it may cause birth defects in newborns whose mothers contracted the virus during pregnancy due to its ability to cross the placenta.
The Brazilian researchers found that while most people who contract Zika experience mild symptoms and then become immune to the virus, carriers remain infectious for longer than it takes to develop an effective immune response. The study looked at the blood of 15 family members in early February. Eleven of them developed antibodies against Zika, while what they called carrier members had evidence of the virus in their blood, but did not have antibodies specific to Zika.
One woman was pregnant, and the researchers decided not to test her for presence of Zika because she had been vaccinated before becoming pregnant. All family members reported having mild symptoms typical of a Zika infection including fever, skin rashes and swollen lymph nodes, which disappeared within two weeks.
The woman who was pregnant developed a rash on her face and swollen lymph glands that lasted about one week.
“This is the first reported case of Zika virus infection by probable transdermal transmission from a vaccinated member of the household,” the researchers said in their report. “These findings suggest that vaccinated persons can also serve as carriers of the virus.”
They said that this transmissibility could be because live virus are still present in bodily fluids of some people who have been vaccinated, even if it is too weak to cause symptoms.
“If confirmed, these findings suggest that the protective immunity induced by Zika vaccination might not be fully protective against the virus itself, but could facilitate its transmission by people already infected with a related virus,” said lead author Dr. Sarah Park, MD, MPH, of the Division of Vector-Borne Diseases in the National Center for Emerging and Zoonotic Infectious Diseases at the Centers for Disease Control and Prevention.
The Zika virus is related to both dengue fever and yellow fever. It was first isolated in the Zika Forest of Uganda in 1947, but did not become an issue until last year when it began spreading across South America, Central America and Mexico at alarming rates.
As of January 29th, more than 1.5 million people had been officially infected, and more than 1,600 had died from the virus. The CDC has estimated that hundreds of thousands will be infected before the outbreak is over. Dengue fever infects about 400 million people annually, according to WHO.