Zika vaccine shows promise in early stage trial

With no Zika vaccine, developing a jab is an 'active area of research'. (Stock, Getty Images) (Manit Chaidee via Getty Images)

A vaccine against the Zika virus has induced an immune response in an early-stage clinical trial, research suggests.

The 2015/16 Zika outbreak in Brazil was one of just six medical incidents to be declared a Public Health Emergency of International Concern by the World Health Organization, with the coronavirus being the most recent.

Spread by mosquitoes, Zika usually causes no symptoms, however, some endure several days of a mild fever, headache and muscle pain.

When caught during pregnancy, the virus has been linked to a host of complications, including microcephaly. This occurs when the brain develops abnormally or there is a loss of tissue in the vital organ, with a child's outcome varying according to the extent of the damage.

Reducing the risk of a Zika infection focuses on avoiding mosquitoes, with no set treatments or preventative therapies.

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With the mosquitoes behind Zika expanding geographically, scientists from Janssen Vaccines and Prevention and the Beth Israel Deaconess Medical Center (BIDMC) gave 100 healthy volunteers their jab candidate or a placebo shot.

Results suggest two doses of the vaccine brought about an immune response that persisted for up to one year in at least 80% of the volunteers.

Zika can only officially be diagnosed via a laboratory test of a bodily fluid, like blood. (Stock, Getty Images) (jarun011 via Getty Images)

Zika has been recorded in 86 countries and territories in Africa, North and South America, Asia and the Pacific. It is not native to the UK.

While most have no symptoms, some develop mild side effects like a rash, red eye and generally feeling unwell between three and 14 days post-infection, with the discomfort lasting up to a week.

Zika can cause abnormalities in a developing baby, as well as a stillbirth or premature labour. The virus was linked to microcephaly in October 2015.

Adults and older children can endure nerve damage, inflammation of the spinal cord and Guillain-Barré syndrome; a rare disorder that occurs when the immune system mistakenly attacks nerves.

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The Zika virus is mainly spread by Aedes aegypti mosquitoes, which can be warded off via insect repellent, keeping doors closed and wearing loose clothing.

The infection can also spread via sex, blood transfusions, organ transplants and from a mother to her baby during pregnancy.

Zika has no vaccine or set treatment, with patients being encouraged to rest, drink plenty of fluids and take painkillers if needed.

Watch: Zika affect foetus' eye development

With the development of a Zika jab an "active area of research", the Janssen and BIDMC scientists have reported the phase 1 results of their vaccine candidate, known as Ad26.ZIKV.001.

The results, published in the journal Annals of Internal Medicine, suggest two doses of the jab is safe and "induced persistent neutralising antibody responses".

Antibodies are proteins that fight off an infection, before circulating at low levels in the bloodstream to help prevent the virus taking hold again. Neutralising antibodies specifically bind to a virus, blocking it from infecting cells.

The antibodies were transferred to mice, which protected the animals when exposed to Zika.

In the human volunteers, the antibody response was maintained for up to one year in at least 80% of those who received two vaccine doses.

These doses were either low or high, suggesting a low dose would be sufficient.

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A single-dose jab induced a lesser immune response, but still brought about "durable antibodies" one year later, "and thus may be a useful tool in curbing future Zika epidemics", according to the scientists.

Zika cases have declined since Brazil's 2015/16 outbreak, however, the "geographic expansion of the Aedes aegypti mosquito to areas where population-level immunity is low poses a substantial risk for future epidemics".

The scientists therefore believe their vaccine "warrants further development should the need re-emerge".

This comes as scientists from Stanford University report screening blood donations for Zika may not be necessary or cost effective, due to the risk of complications from this method of transmission being "exceedingly low".

Watch: Zika-carrying mosquito species in California