Zika Causes Birth Defects, But How Fast Can A Vaccine Be Developed?
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The CDC announced yesterday what most public health officials have already taken for granted for several months now: Zika causes microcephaly. I reported on one of the strongest pieces of evidence back in February, when some experts had already come to this conclusion. More recent evidence has also revealed the virus can cause stillbirth, miscarriage and other birth abnormalities aside from microcephaly, which the CDC included in their announcement.
“This study marks a turning point in the Zika outbreak,” CDC director Tom Frieden, MD, said in a prepared statement. “We are also launching further studies to determine whether children who have microcephaly born to mothers infected by the Zika virus is the tip of the iceberg of what we could see in damaging effects on the brain and other developmental problems.”
Public health workers have been struggling to address the threat of Zika since the first microcephaly cases following infection were reported in Brazil last year. Currently, primary preventive approaches are focused on controlling mosquito populations and protecting individuals, using repellent, screened windows and air conditioning. But the best approach, as Dr. Peter Hotez of Texas Children’s Hospital Center discussed in January, would be a vaccine.
Easier said than done. Despite hopes of having a vaccine “within months,” as the head of the National Institute of Allergy and Infectious Diseases claims is possible, vaccines typically take years to develop, explained Jay Nelson, PhD, a senior molecular virologist and founder and director of the Vaccine and Gene Therapy Institute at Oregon Health and Science University. He agreed that a vaccine is the most efficient and effective way to protect people, especially now that the virus appears to have mutated and poses a big threat to pregnant people and developing fetuses. But Zika is about 40% homologous to the dengue virus at the amino acid level, he explained, and a dengue vaccine has taken two decades to develop—and there still is not a highly effective, safe dengue vaccine.
Given the number of groups working on Zika vaccine development, however, it hopefully won’t take 20 years to develop one.
“There are probably more than a dozen groups,” Nelson said of those working on a vaccine across the world. “I think everybody and his mother are working on this right now.”
The first hurdle, he said, is to find an appropriate animal model for Zika testing. Mice are cheapest, but the Zika virus doesn’t replicate in wild mice. Nelson’s lab is currently using rhesus macaques, the same primate in which scientists first identified the virus in the Zika jungle of Uganda in the 1940s. They have managed to infect the monkeys with the virus so that the virus is circulating in the primates’ blood, but it’s not causing disease in the monkeys, which could make it harder to determine how effective the vaccine is. Still, they’re moving forward by seeing what an infection does in vaccinated macaques who are pregnant.
“We’re trying to determine whether this virus crosses the placenta in a non-human primate and whether it causes disease in the fetus,” Nelson said, and they’ve brought together multiple departments to work together on understanding Zika. “We have people that are looking at the neurodevelopment, the placenta, infections, the developing fetus in the primate, the innate system and the development of vaccines and antivirals.”
Effectiveness must also be balanced with safety: the most effective vaccines are attenuated live virus vaccines, which allow the virus to replicate but not cause disease. But these can carry more risks for groups with less effective immune systems, such as those with immune deficiencies, those taking immunosuppressants and adults over age 55. Another challenge to developing a safe vaccine is Zika’s link to the nerve disorder Guillain-Barré syndrome. If the virus can cause Guillain-Barré, it’s important to be sure a vaccine using the virus doesn’t increase the risk of the disorder in those vaccinated.
The infographic below describes the hurdles a Zika vaccine must clear before it makes it to market. It remains to be seen how quickly scientific collaboration can get it across the finish line.
“A hell of a lot of people are working on this as fast as they can,” Nelson said. “As bad as this disease potentially is, the good thing about it is that it’s brought together many scientists from many different disciplines to work together. It takes a team of people to do this, not just one person.”