The Zika epidemic will be around for the next three to five years and then disappear – but this won’t be the last of it, according to leading scientists who spoke at the recent International Congress of Immunology in Melbourne.
In 10 to 15 years, there will be a “second wave”, suggests Brazilian immunologist Professor Jorge Kalil, director of the Butantan Institute, Brazil’s largest producer of immunobiological products. So while efforts to develop a vaccine against the Zika virus may not reach fruition in time to benefit the current wave of infected people, it could still be beneficial in future.
The predictions of Zika’s “burn out” is based on mathematical models, explains Professor Cameron Simmons of the Peter Doherty Institute for Infection and Immunity in Melbourne. Analysing available data around Zika virus transmission, as well as what is known about dengue viruses – which are spread by the same vector, the Aedes aegypti mosquito – scientists are able to predict what Zika’s trajectory might look like.
“In the next three to five years, such a large proportion of the susceptible population will be infected and immunised – when you get infected you become immune to the virus,” Simmons says. “Once a critical threshold of the population has been infected, the virus cannot find anyone new to infect, and so virus transmission collapses. What is required for significant transmission to occur again, is for the birth cohort to build up, so that the fraction of susceptible people increases over time.”
Kalil adds that because there is only one serotype of the Zika virus compared to four serotypes for dengue, it is unlikely Zika will stick around for many years like dengue.
“I think Ebola is same game,” says Simmons. “The epidemic in West Africa is finished, but it’s not stopping the development of vaccines because we know there’ll be a next time.”
To call the race for a Zika vaccine intense would be an understatement. All over the world, researchers are investigating various ways to inoculate against the virus. Kalil himself is involved in a few developments.
One project works with inactivated vaccines, where the virus is produced, then killed and used to obtain antibodies that would neutralise the live virus. The advantage of such a vaccine is it usually does not take long to be approved by regulatory authorities, Kalil says. “If we want to do something for females who will get pregnant in these few years, we have to be very quick,” he says.
Another type of vaccine that could progress very quickly with few safety issues is a DNA vaccine, which uses genetically engineered DNA to generate an appropriate immune response.
Kalil is also working on an attenuated, or weakened, form of the virus to make a vaccine. “But this type of vaccine will take a long time and should be used for people that could be threatened by the second wave of the virus in 10 to 15 years,” he says.
Scientists are also working on developing antibodies that could neutralise both Zika and dengue. In a study published in the journal Nature in June, an international team of scientists in Paris, London and Vienna identified these antibodies and revealed the antibody binding site for both viruses to be identical, opening up the possibility of development of a universal vaccine for dengue and Zika.
“One idea could be to give antibodies to all females who get pregnant in hyperendemic areas, and not wait for them to get Zika infection,” Kalil says.
On a different front, Simmons is involved in a large research project that uses Wolbachia bacteria to make Aedes aegypti mosquitoes resistant to dengue, Zika and chikungunya viruses. Results from studies in five countries show this method to be effective in controlling the vector, Simmons says, and gold standard cluster randomised trials in Vietnam and Indonesia will start soon.
Until a vaccine is successfully produced, Simmons says “old-fashioned tools” such as vector control through finding and destroying mosquito breeding sites, heavy-duty fogging and advising personal protection is going to be the “bread and butter of control for the next one or two years at least”.