Since 2016, when the World Health Organization (WHO) called for prioritising the development of vaccines against the mosquito-borne disease Zika, research has taken place around the world but no vaccine has been approved yet.
This week, two teams have separately reported vaccines they have or may have identified, one of these with the promise of overcoming what has been seen as a possible stumbling block so far. The news, incidentally, came at a time when a Zika outbreak in Rajasthan has led to the United States issuing an alert asking pregnant women not to travel there.
While a vaccine against Zika would create protective antibodies against the virus, many studies show that antibodies against Zika virus can worsen dengue virus infection, which too is mosquito-borne. Known as antibody-dependent enhancement (ADE) of disease, this phenomenon has been an obstacle to the development of effective and safe dengue virus vaccines, the University of Nebraska-Lincoln observed in a statement announcing the possible identification of a vaccine that gets around this obstacle. The research is published in the journal Scientific Reports.
The team may have identified a vaccine that would defend against Zika virus without producing antibodies, the statement said. It quotes researcher Eric Weaver as saying: “If you have immunity to one of these viruses and get infected by a second one, the illness can be much worse. The body makes the wrong immune response.”
Now that the potential vaccine does not produce antibodies, Weaver said: “If we can figure out the mechanism, we might be able to apply it to other vaccine strategies. This would be a huge leap for immunology and vaccine research.”
The scientists used two forms of weakened Adenovirus to serve as vectors to deliver the Zika vaccine. They inserted structural genes of Zika into genomes of two types of Adenovirus. Tested in mice, the two vaccines offered strong responses and substantial protection against Zika infection, and one vaccine induced strong responses with undetectable antibodies.
“To our knowledge, this is the first report of a vaccine that uses the prM-E genes of Zika virus to induce protective immunity without inducing anti-Zika virus antibodies. The lack of antibodies may very well circumvent the potential risks of ADE, resulting in an effective and safer vaccine than those currently in clinical trials,” the statement quoted Weaver as saying.
The other potential vaccine was announced in a press release by KU Leuven Rega Institute, Belgium. Describing it as safe, it said the vaccine should prevent the virus from causing microcephaly and other serious conditions in unborn babies. It was tested successfully in pregnant mice.
The team said they made use of the yellow fever vaccine, which is closely related to the Zika virus and is transmitted by the same mosquito. “We replaced a piece of the genetic information of the yellow fever vaccine with the corresponding code of the Zika virus. To engineer the vaccine, we used a new technology that we’d developed earlier in our lab and that makes it possible to produce the vaccine in fermenters instead of in fertilised chicken eggs,” the university quoted researcher Johan Neyts as saying.