Phase 2 Zika Vaccine Trial Begins in US, Along with Central & South America

Phase 2 of a Zika vaccine trial began in the United States this week, along with Central and South America.

The vaccine was developed by expert scientists at the National Institute of Allergy and Infectious Diseases (NIAID), which is part of the National Institutes of Health, the country's primary medical research agency. There will be around 2,490+ healthy participants in the study, all of whom live in high-risk areas, including parts of the US, as well as Puerto Rico, Brazil, Peru, Costa Rica, Panama, and Mexico.

Zika is spreading at an alarming rate, with the Centers for Disease Control and Prevention (CDC) issuing travel notice warnings for Cape Verde, Mexico, Singapore, and multiple countries in the Caribbean. Zika virus is transmitted by the Aedes aegypti mosquitoes, which are prevalent throughout the southern US, many US territories, and many tropical climates. It can also be spread in semen.

Zika symptoms include fever, rash, joint pain, and red eyes. Infected people can exhibit less extreme symptoms, which doctors have labeled as "mild." However, cases of Guillain-Barré syndrome, where a person's immune system attacks their own nerves, have also been reported.

In developing fetuses, though, the Zika virus inhibits nerve cells, delaying cell growth in developing brains and causing cell abnormalities and cell death. Infants born to infected women could develop microcephaly, which results in small heads and nervous system disorders. There has been an estimated 1,900% increase in this condition in the US from last year when compared to 2013–2014.

The first healthy volunteer receives the NIAID Zika virus investigational DNA vaccine as part of the vaccine trial.

The Zika vaccine contains a piece of DNA (called a plasmid) into which two genes that encode two proteins found on the surface of the Zika virus were inserted. These proteins assemble into particles that mimic Zika when they are injected into muscle. The participant's immune system will then respond and hopefully create antibodies against the proteins, which will also protect them against infection with the live virus if they get bitten by a Zika-infected mosquito.

The purpose of this trial, which is called VRC 705, is twofold: First, the researchers need to establish the safety of the vaccine, and determine the optimum dosage and analyze how peoples' immune systems respond to it. Secondly, they'll determine whether the vaccine can prevent the Zika infection.

The first part of the test will involve 90 healthy men and non-pregnant women aged 18–35 years in Houston, Miami, and San Juan, Puerto Rico. Volunteers will be tested with both a low and a high dose (which is first chosen randomly) three times, four weeks apart, for 32 weeks in total.

In the second half of the test, 2,400 healthy men and non-pregnant women, aged 15–35 years, will be injected to see whether the vaccine protects against the virus in areas of high exposure, including the sites tested in the first half of the study. Additional testing sites include San Juan, Costa Rica (2 sites), Peru Brazil, Panama, and Mexico (1 site each). These people will be monitored for two years to see if they get a Zika infection.

Speaking about the process in a press release, NIAID Director Dr. Anthony S. Fauci said:

We are pleased to have advanced rapidly one of NIAID's experimental Zika vaccines into this next stage of testing in volunteers. We expect this study will yield valuable insight into the vaccine's safety and ability to prevent disease caused by Zika infection. A safe and effective Zika vaccine is urgently needed to prevent the often-devastating birth defects that can result from Zika virus infection during pregnancy. Evidence also is accumulating that Zika can cause a variety of health problems in adults as well. This trial marks a significant milestone in our efforts to develop countermeasures for a pandemic in progress.

The trial is entering the human testing phase after extensive trials on animals showed it exhibited a neutralizing antibody response to the disease, which stops the virus from being able to infect the body's cells.

This is welcome news considering the frequency of Zika in recent years. Just last week, a baby with severe microcephaly (symptomatic of congenital Zika syndrome) was born in Florida after its mother contracted the disease abroad.

Example of microcephaly on the left, compared to a normal baby's head on the right.

According to the CDC, 54 infants have been born in the US with severe Zika-related defects as of March 14, 2017. Meanwhile, there were 296 cases of Zika reported in the US since January 2015 that originated from within the country, and these were largely confined to Florida and Texas. However, more than 4,800 people returned from abroad to the US with the virus in tow.

Preventative measures include avoiding travel to areas of high risk, avoiding insect sites, wearing repellant, and using condoms or abstaining from sexual activity to lesson the risk of contraction.

If you have questions about VRC 705 Phase 2/2b Trial, there's answers available from NIAID, as well as more information.

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Cover image by NIAID/NIH