When it comes to infectious diseases, mosquitoes win. Last year, health officials reported a spike Dengue has also recorded infections in and even nontropical areas, where the disease is not normally endemic. Malaria is resurgent in parts of the north and south America, AfricaAnd Asia. even Anthony FauciA nasty case of West Nile, former director of the National Institute of Allergy and Infectious Diseases Mosquitoes in his backyard In DC
Some of the increase can be explained by the increase of mosquitoes in new places due to changes in temperature and rainfall. Mosquitoes and the pathogens they carry are also developing resistance to pesticides and drugs previously used to eradicate them.
This story first appeared in the Future Perfect Newsletter.
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The US government and other global health donors have invested billions in developing new vaccines and drugs for mosquito-borne diseases dengue, MalariaAnd Chikungunya. One virus, however, that has faded into the background still has no vaccine and no cure: Zika.
In 2015The Zika virus — which previously rarely infected humans — suddenly spread rapidly, causing million Case more than two years. Worse, scientists noticed an alarming phenomenon: A small fraction of infected pregnant women gave birth to babies with what became known as congenital Zika syndrome, characterized by severe birth defects Such as hearing and vision loss, feeding problems and MicrocephalyA neurological condition in which children have abnormally small heads. In Brazil, which was hit hardest by the pandemic, even more so 3,500 Babies were born with Zika-related birth defects.
Fortunately, the number of Zika infections worldwide has declined rapidly since the end of 2016, although the causes are still largely unknown. A leading theory is that the virus spreads so quickly that communities thrive Herd immunity. Or perhaps mosquito control efforts, such as spraying insecticides and encouraging communities to eliminate standing water sources, have obliterated the transmission of the virus. There is the continental US Not recorded No cases since 2018 and US territories since 2019.
Unfortunately, as Zika cases have decreased, so has global funding and interest in Zika. Public health officials and, more importantly, donors and policymakers have turned to other priorities, including the impending COVID-19 pandemic. No Zika vaccine has ever come to fruition.
Despite waning attention, Zika is still spreading in many countries. In the first half of 2023, health officials recorded approx 27,000 Brazil is the country most affected by Zika infection in the Americas 2,700 Lawsuits Thousands of babies are still being born with preventable disabilities.
“With a safe and effective Zika vaccine, we can eliminate the possibility of congenital Zika syndrome, and I think that will have a huge impact,” said Anna DurbinProfessor of International Health and Global Disease Epidemiology and Control at Johns Hopkins University. “Although there are few cases of congenital Zika syndrome, the emotional, financial impact is huge.”
Scientists and global health experts to warn That Zika, along with other mosquito-borne infectious diseases, could cause a widespread resurgence. The first step to defeating the epidemic is prevention, and a Zika vaccine is vital to that goal.
But big obstacles stand in the way. Private pharmaceutical companies are reluctant to invest in vaccine development because so few people are now being infected – and those who are becoming infected live mainly in relatively poor countries. Researchers say the government is not investing enough public funds in vaccine development. And running a traditional clinical trial is nearly impossible for the few vaccines that were hastily developed during the 2015 outbreak.
A brief history of Zika
Within the first month 2015Doctors in Brazil have noticed a sudden increase in patients with a strange skin rash. They warned the World Health Organization (WHO) that an unknown infectious disease might emerge. in a a few monthsScientists identified the cause of the outbreak: zikaA virus was first discovered in the Zika forest in Uganda 1947 which is spread by certain types of mosquitoes.
At first there was no cause for concern. Since 1960sThe virus has only caused sporadic infections in Africa and Asia, and then in the Americas. Furthermore, Zika almost never causes symptoms 80 percent For those infected, others usually experience only mild illness characterized by low-grade fever, skin rash, and conjunctivitis. By March 2015, er 7,000 Or so those who developed skin rash in Brazil, no one died.
But then in SeptemberBrazilian doctors are beginning to notice an alarming new pattern. Somewhere in the middle 2 percent And 6 A percentage of babies born to Zika-infected women had small, malformed brains, called brains Microcephaly. Other Children were missing key brain structures or had other defects. Doctors call it congenital Zika syndrome.
To make matters worse, the virus quickly spread beyond Brazil’s borders. Pan American Health Organization in December announced The Zika outbreak is an international health emergency. WHO followed suit February By the end of next year 201648 countries and territories across North and South America are reporting cases.
Funding for outbreak response surged. The US government has given up alone $1.1 billion Supporting activities such as surveillance, education, mosquito control, and vaccine research. Various studies groupAround 40 vaccine candidates have been developed, mostly in the US, UK and South Korea. A handful of those vaccines have gone through small phase 1 and 2 clinical trials and appear promising. Dan BaruchA professor of immunology at Harvard Medical School, retracted.
Then suddenly the outbreak subsided. Countries stopped reporting Thousands of cases From every few months in 2016 to just a few, sporadic events in 2017.
This was, obviously, a good thing. Unfortunately, though, once a disease poses a minimal threat to high-income countries, where most research and development occurs, progress toward developing effective vaccines and drugs stalls. Governments, scientists and pharmaceutical companies shifted funding and attention to the next health emergency, leaving low-income countries in the global south to fend for themselves.
But the rapid rise and fall of the Zika outbreak has created another challenge. Two years after the outbreak, when candidate vaccines were ready for real-world testing, there were no longer enough susceptible people for Phase 3 clinical trials.
Why Zika Vaccine Development Has Stalled
Before that a regulatory agency like the US Food and Drug Administration could approval For a new vaccine, it must generally be proven safe and effective Phase 3 clinical trials. Hundreds of thousands of people are vaccinated and then monitored to measure the effectiveness of the dose if some people develop the disease. So researchers need a large pool of people willing to be in a trial and potentially exposed to the disease.
In the first year or so of the 2016-2017 Zika outbreak, there were enough people to warrant such a trial. But researchers first had to complete smaller phase 1 and 2 trials, which focused primarily on safety. By the time some vaccines were ready for phase 3 trials, outbreaks were too small to provide enough subjects.
Even today, when Zika sporadically pops up around the world, there are usually only a few hundred cases at any given time, and researchers can’t pinpoint where and when cases will appear. They can’t start a trial yet, Durbin explained.
There are alternative pathways for a vaccine to be approved that do not require phase 3 clinical trials. According to Durbin, drug developers don’t want to cover those costs because they’re unlikely to recoup them, given how few people are getting Zika now.
A lack of government funding for vaccine research and development is compounding the problem. Government funding for various diseases comes with outbreaks, first for Ebola then for Zika and then for Covid-19.
On the bright side, if another large-scale Zika outbreak were to occur, scientists already have a handful of vaccine candidates ready for large clinical trials. Scientists and vaccine manufacturers still need to develop enough vaccine for a large trial and get approval from authorities and policy review boards in whatever country the trials are taking place.
Although infections are much lower than in 2015 and 2016, Durbin said there is still an urgent need for a vaccine.
“Women living in Brazil during this outbreak were terrified if they got pregnant, absolutely terrified of what would happen to their babies,” he said. “It will provide peace of mind.”
Peace of mind for mothers in the global south, however, is not enough to move the big pharmaceutical companies.
