The World Health Organization has declared the Zika virus—transmitted by mosquitoes—a “global public emergency,” and has called on different governments and medical communities to combat the spread of the disease and develop a vaccine. The U.S. National Institutes of Health, the Public Health Agency of Canada and the Butantan Institute in Brazil have all started work on potential candidates for a Zika vaccine, and several biotech firms are similarly at work. The question then becomes: How quickly can they develop such a vaccine?
Most people with a Zika infection may not even present symptoms. However, there is a growing body of evidence linking Zika infection in pregnant women with an increased risk of their babies being born with microcephaly. This condition results in an abnormally small head impairing brain development.
The front-runner in Zika virus vaccine development may well be French company Sanofi Pasteur, which announced it has launched a vaccine research and development project targeting the prevention of Zika virus infection and disease. The company is the vaccines division of Sanofi, and has previously developed licensed vaccines against Yellow Fever, Japanese Encephalitis and, most recently, Dengue. That’s important because Zika is closely related to Dengue: they belong to the same Flavivirus genus, are spread by the same species of mosquito and have a similar acute clinical presentation. Consequently, the company’s experience, established R&D and industrial infrastructure for the newly licensed vaccine for Dengue, Dengvaxia, can be leveraged to help understand the spread of Zika—and, potentially, speed identification of a vaccine candidate for further clinical development, says Dr. Nicholas Jackson, Global Head of Research for Sanofi Pasteur.
“We really hope to significantly reduce that timeline and cut years off the typical amount of time it takes to develop a vaccine,” Dr. Jackson says. “We have a jump start here because we have an infrastructure that we’ve put in place around our Dengue vaccine that we can tap into very quickly.”
In theory, creating a vaccine to generate an immune response against Zika virus shouldn’t be too difficult. Practically, however, there are numerous significant challenges.
“To be useful, a Zika vaccine would need to be effective and safe, but it's difficult to do both,” Ben Neuman, an expert on viruses at Britain’s University of Reading, says in a Reuters story. “It’s a balancing act.”
Vaccines work by provoking a person’s immune system into creating a strong response, but no so strong as to make them sick. The crucial target group for a possible Zika vaccine is women who are, or may become, pregnant. The largest challenge for a possible vaccine is that pregnant women are typically excluded from clinical trials until the safety of new drugs or vaccines is well-established in other population groups. It also makes for an uncertain, and potentially limited, market for any Zika vaccine.
On the other hand, although pregnant women are the focus of concern due to the virus’ association with a possible birth defect, Dr. William Schaffner, an infectious disease expert at Vanderbilt University, says in an ABC News report that they would probably not be the first ones to get the vaccine.
“Although we’re interested in protecting pregnant women, I think the actual strategy would be able to give vaccine to as many people in the population as possible,” Dr. Schaffner says. “It would reduce the risk of the mosquito becoming infected,” and spreading the disease to pregnant women.
That approach makes sense, not only to minimize the number of infected people that mosquitoes could bite, but also to prevent the spread of the Zika virus by other means. Investigators have been exploring the possibility the virus also can be spread through sex because there are reports of a patient in Texas and another in Colorado who acquired the Zika virus through sexual contact with an ill person who returned from a country where Zika was present.
What other challenges do you see for companies or consortia working on a Zika vaccine?