Over the past several weeks, the Zika virus has morphed from an obscure disease into an international public health emergency, gaining global attention. This has left the public health research community with many questions; Where did the disease originate? How is it transmitted? How do we work together to develop and distribute a vaccine?
In this blog we'll explore the existing information surrounding the Zika virus and some of the challenges associated with vaccine development.
What is the Zika virus?
The Zika virus is a mosquito-transmitted infection and is categorized as a flavivirus, related to dengue, yellow fever and West Nile virus. Aedes mosquitoes, which typically bite in the morning and late afternoon/evening, transmit the virus. According to the Centers for Disease Control and Prevention (CDC) about one in five people infected with the Zika virus become ill and while the incubation period is still unknown, it can likely last several days. While mosquitoes are its vector, Zika’s viral reservoir is also unknown.
The Zika virus can cause Zika disease, which may include the following symptoms:
- Mild fever
- Maculopapular skin rash
- Muscle and joint pain
These symptoms typically last for 2 to 7 days. The virus remains in the blood for about one week but may stay longer in some people. While the Zika virus causes only mild and short-lived symptoms with no aftereffects for most people, some mothers infected with the Zika virus during pregnancy appear to have given birth to babies with microcephaly. Microcephaly can cause babies to have smaller heads than other babies their age and is also associated with incomplete brain development and neurodevelopmental disorders.
Microcephaly is rare and while it has been linked to other diseases such as rubella, toxoplasmosis, and diabetes, the correlation to Zika virus is a recent discovery. This is likely due to the fact that the virus was contained within Asia and Africa for about 50 years, where populations were battling other painful infections such as dengue and chikungunya. However, in 2007 the virus spread to islands throughout Southeast Asia where there was no immunity. As the symptoms affecting the population began to increase, the correlation between microcephaly and Zika virus became more evident.
The History of Zika
Scientists first identified the Zika virus on April 18, 1947, when a caged rhesus monkey living on a tree platform in the Zika Forest in Uganda developed an unknown febrile illness. The CDC reports that the monkey, Rhesus 766, was "a sentinel animal in the Rockefeller Foundation’s program for research on jungle yellow fever." The scientists isolated the transmissible agent and dubbed it ZIKV, or Zika virus. Researchers found that same virus in an Aedes africanus mosquito captured in the Zika Forest about a year later.
ZIKV appeared in humans in 1952 in Uganda and the United Republic of Tanzania. Zika disease remained within Africa and Asia until April of 2007, when an outbreak of rash, arthralgia, and conjunctivitis occurred on Yap Island in the Federated States of Micronesia.
Zika already exists in Africa, Asia, the Pacific and now, the Americas. In fact, the World Health Organization (WHO) says that more than 13 countries in the Americas have reported sporadic infections of the Zika virus. Increasing spread of Zika is most likely to occur in the Commonwealth of Puerto Rico, the U.S. Virgin Islands, Caribbean or Pacific territories, and Central and South America, where the mosquito flourishes. Large outbreaks have occurred in French Polynesia and Brazil in 2013 and 2015, respectively. People living in crowded communities without air conditioning or mosquito repellent are most susceptible to infection.
Why Isn't There a Vaccine for the Zika Virus?
It costs $160-500 million USD to develop a vaccine, which pales in comparison to the ethical, social and financial considerations of microcephaly. So why is there no vaccine for Zika virus?
Until the recent Zika outbreak, vaccine developers have put their resources towards developing vaccines for other severe and potentially fatal mosquito-borne diseases, such as malaria, West Nile virus and dengue. To complicate matters further, only a small number of scientists have studied ZIKV, so drug developers have very few tools to work with. And while a handful of labs have the Zika virus, these labs have now received hundreds of requests from researchers trying to develop vaccines and treatments for Zika disease.
The ideal vaccine would elicit a strong response from the immune system, provide long-term protection with few doses and cause no side effects. Developing such a vaccine is no easy task, as vaccines often look promising in pre-clinical testing but fail during the slow and costly process of clinical trials. Researchers hoping to develop a vaccine must determine which immune response will provide the best protection against the virus. Vaccine safety is also a major concern, as attenuated vaccines provide superior protection but live vaccines present a greater potential to cause disease rather than prevent it.
It typically takes 10 to 15 years to develop a vaccine. Development begins with identification of an antigen that can prevent disease and securing clearance from the U.S. Food and Drug Administration (FDA) for further testing. Next, researchers put the vaccine through at least three phases of human clinical trials to assess efficacy, determine dosage and monitor for side effects. Finally, drug developers perform years of research, development and testing to gain FDA approval. One way to speed up this process is through the FDA Fast Track Development Program. Many researchers are looking to this as a way to mitigate the spread of life threatening illnesses by expediting the review process.
Several companies are working to develop a vaccine for ZIKV. Many are utilizing existing vaccines by stitching proteins from the pathogen’s surface onto a known harmless virus or vector. This phase of development usually takes 10 to 15 months but the urgency of the Zika outbreak may shorten that timeline. Even so, Dr. Anthony Fauci, the director of the National Institute for Allergy and Infectious Diseases says it could take five to seven years to develop a vaccine for ZIKV.
There are still a lot of unanswered questions about the Zika Virus, but as researchers continue to work towards developing a vaccine the importance of distribution is sure to follow. To learn more about how Fisher BioServices developed a qualified cold chain transport solution to transport vaccines to Uganda, download our Case Study below.