Amid the depressing news about Zika continuing to infect more people and spread quickly, there is some good news. Three vaccine candidates have been shown to work successfully in monkeys and one is being tested in a human trial, raising hopes that a vaccine may soon be available on the market.
But don’t get your hopes too high. Even with such success stories, it is unlikely that any Zika vaccine will be available this year or even early next year. That’s because developing a safe and effective vaccine is difficult in the best of times, and gets harder during an epidemic. Consider the example of Ebola.
The Ebola epidemic began in west Africa in early 2014. By the time the World Health Organization (WHO) declared in June 2016 that it was over, the disease had infected 28,000 people and killed 11,000.
Ebola had been on the radar of public-health officials for many years and we even had some vaccine candidates lying on scientists’ shelves before the epidemic. Once the WHO declared Ebola a public-health emergency, scientists began working with renewed urgency and funding. Two years on, some vaccine candidates have reached the very last phase of clinical trials. Sadly, however, none have yet been approved to be sold on the market.
There are many reasons why, despite much scientific progress, we are still unable to develop vaccines in a timely manner.
When a new disease starts spreading, it often spreads unchecked before raising alarm. And the pathogen often spreads in places where health infrastructure is not good, such as Ebola starting in Guinea. So by the time we are aware that an epidemic has taken hold, the pathogen is many steps ahead of the humans trying to stop it.
We live on a planet of microbes. The microbe behind every new epidemic is wildly different from the previous one. For instance, even though Ebola and Zika are both caused by viruses, they are completely different beasts. To develop a successful vaccine, we need to understand the pathogen quickly, see if there is more than one genetic strain of it that is causing the disease, and then develop means to counter each strain. But chaotic epidemics can make it difficult to collect the necessary samples and send them to labs.
Big pharma companies invest billions in research every year, but few jump to action when there is urgent need for vaccines. Though such companies regularly make losses on failed drug candidates, they are often able to claim some return on investment by applying lessons learned and expertise gained in new projects. However, most can’t follow that process for vaccine developments, because they don’t have other vaccine projects that can carry over the learning.
If big pharma won’t take the lead, you’d expect the WHO to do so. Even though the WHO’s constitution states that its objective “is the attainment by all people of the highest possible level of health,” the WHO hasn’t been setup to coordinate research programs. Research programs require huge sums of money and the WHO doesn’t have it. All it does now is create a framework for how research must be conducted on a new disease and then it hopes that various national health bodies will use the framework to do the work.
Once the pathogen causing an epidemic is identified, scientists need to find a good animal model to test early vaccine candidates. The most commonly used model is small mammals, like rats or mice. But they don’t always get infected by a pathogen that has specialized to infect humans. For instance, it took nearly two months to develop the first animal model for Zika after the WHO declared a public-health emergency.
Despite all these difficulties, some vaccine candidates do make it through to human trials. But here they linger for longer than we’d like. The first human trial for the most promising Ebola vaccine candidate started in November 2014. Despite success, by June 2015, the company was struggling to find enough human volunteers to continue its trials, because the disease had passed its peak.
Clinical trials start with tens of patients. With success in each phase, the trial is expanded—from hundreds to thousands to, finally, tens of thousands. However, at each phase, scientists have to collect a lot of data and analyze it to be sure that the vaccine is doing what it should in humans and there are no nasty side effects. This takes time, and in that time often an epidemic crosses its peak. So even though the trial needs more patients, there often aren’t enough around to test the vaccine on the scale needed to approve it for commercial use.
So although it’s great news we are making progress on a Zika vaccine, it won’t be ready any time soon to stop the disease spreading. Still, given it normally takes more than 10 years to develop a vaccine, it’s a small miracle that we can get close to developing one in an emergency in less than three years.