Vaccines
The National Institute of Allergy and Infectious Diseases (NIAID) is currently investigating a variety of Zika vaccines, including a DNA-based vaccine, (phase 2), a purified inactivated virus vaccine (phase 1), live attenuated vaccines (phase 2), and mRNA vaccines (phase 2).
“I’m most excited about mRNA vaccines because they help patients produce a lot of proteins. The protein from a typical protein-adjuvant vaccine will break down, and patients can only raise an immune response to whatever proteins are left. On the other hand, mRNA vaccines provide the body [with] a recipe to make the protein from the pathogen in high amounts, so that a strong immune response can be raised for protection,” noted Dr. Gandhi.
Moderna’s mRNA-1893 vaccine was recently studied in a randomized, observer-blind, controlled, phase 1 trial among 120 adults in the United States and Puerto Rico, the results of which were published online in The Lancet. “The vaccine was found to be generally well tolerated with no serious adverse events considered related to vaccine. Furthermore, the vaccine was able to generate a potent immune response that was capable of neutralizing the virus in vitro,” said Brett Leav, MD, executive director of clinical development for public health vaccines at Moderna.
“Our mRNA platform technology ... can be very helpful against emerging pandemic threats, as we saw in response to COVID-19. What is unique in our approach is that if the genetic sequence of the virus is known, we can quickly generate vaccines to test for their capability to generate a functional immune response. In the case of the mRNA-1893 trial, the vaccine was developed with antigens that were present in the strain of virus circulating in 2016, but we could easily match whatever strain reemerges,” said Dr. Leav.
A phase 2 trial to confirm the dose of mRNA-1893 in a larger study population is underway.
Although it’s been demonstrated that Moderna’s mRNA vaccine is safe and effective, moving from a phase 2 to a phase 3 study presents a challenge, given the fact that currently, the disease burden from Zika is low. If an outbreak were to occur in the future, these mRNA vaccines could potentially be given emergency approval, as occurred during the COVID pandemic, according to Dr. Silverman.
If approved, provisionally or through a traditional route, the vaccine would “accelerate the ability to tamp down any further outbreaks, because vaccine-based immunity could be made available to a large portion of the population who were pregnant or planning a pregnancy, not just in the U.S. but also in these endemic areas,” said Dr. Silverman.
Takeaways from the last Zika outbreak
Practical steps such as mosquito eradication and development of vaccines are not the only takeaway from the recent Zika epidemics inside and outside the United States. A clearer picture of the short- and long-term stakes of the disease has emerged.
According to the CDC, most people who become infected with Zika experience only mild symptoms, such as fever, rash, headache, and muscle pain, but babies conceived by mothers infected with Zika are at risk for stillbirth, miscarriage, and microcephaly and other brain defects.
Although a pregnant woman who tests positive for Zika is in a very high-risk situation, “data show that only about 30% of mothers with Zika have a baby with birth defects. If a pregnant woman contracted Zika, what would happen is we would just do very close screening by ultrasound of the fetus. If microcephaly in utero or fetal brain defects were observed, then a mother would be counseled on her options,” said Dr. Gandhi.
Dr. Silverman noted that “new data on children who were exposed in utero and had normal exams, including head measurements when they were born, have raised concerns. In recently published long-term follow-up studies, even when children born to mothers infected with Zika during pregnancy had normal head growth at least 3 years after birth, they were still at risk for neurodevelopmental delay and behavioral disorders, including impact on coordination and executive function.
“This is another good reason to keep the potential risks of Zika active in the public’s consciousness and in public health planning.”
Dr. Silverman, Dr. Gandhi, and Dr. Staples have disclosed no relevant financial relationships. Dr. Leav is an employee of Moderna and owns stock in the company.
A version of this article originally appeared on Medscape.com.