Localised trials of three different Zika vaccines in healthy adults have already seen benefits last long according to the first study of its kind which was carried out in the USA.

Researchers found that tandem vaccine (TIV) which is accepted by both the pharmaceutical and public health communities in the journal Nature Microbiology can protect people for up to six months from exposure to the virus even when the dose increases daily.

Current Zika virus vaccines range from doses of two to four a year where the minimum is 10.

Italian-US company Viravax financed by the National Institute for Health Research (RIVAUniVenecia) in partnership with Bio Bioscience has spent up to 100 million on developing the vaccine.

The field of Zika virus vaccine development relies on trivalent vaccine which are sets of three shots in a row. A booster is added each year.

Lead author Dr. Borone Lipman National Institute for Health Research Lausanne Switzerland said: Recently we showed that a single dose of TIGV vaccine can extend immunity in adult volunteers even with a two-dose regimen. Full immunization with the TIGV vaccine is however not achieved until at least 10 years later.

In this study we used our most powerful tools: randomized controlled trials. In such studies vaccines are fitted to individual populations and the results are compared with those of control groups with no vaccine. In this way we integrate the indication of the intervention and its prevalence into the overall scientific position for vaccine efficacy.

Study authors tested the efficacy of the trivalent vaccine in 11 adult volunteers who were both vaccinated and who were either unexposed to the virus or unexposed and who were then vaccinated with the TIGV vaccine. WAVES (Total Immunised Influenza Vaccine Study) is a prospective observational study also carried out in Italy.

Surveillance and player-neutralisation studies require a test group with the intent of finding efficacy and a control group which is the most appropriate for women who may not have been vaccinated.

The trial in the USA involved 412 participants with no history of exposure to the Zika virus 627 with an exposure history and 929 with no exposure.

Instead of repeating the usual standard of randomization with allocation of risk and control groups this trial was designed to test the k-fold rule in terms of dose-response said Lipman.

Levels of scientific evidence on MERS chikungunya fever and Dengue fever were grouped into three vaccine types: TIV (NIV) IIV (ACVB) and MACV (LIG). Several vaccine types showed a higher level of neutralising antibodies than in control groups nearly matching the levels found in the control group. Typical neutralising antibodies are 100-200 IUml with neutralising activity ranging from 80-100 IUml.

The level of neutralising activity in vaccinated groups was over 90 at six-month intervals and 90 at 12 months. On the other hand levels of neutralising activity were found to be high in the placebo-treated group only with more than 100 IUml in the placebo-treated group or higher in the placebo-treated group in some cases Lipman said.

The reason for these differences is that the recent elimination of MERS virus from the Ukraine but not in the US is not yet convincing a particularly disappointing result. In dealing with the ongoing outbreaks of severe acute Miami disease we need to remain more cautious and use caution in using different parameters to define immunity and suppress the false feelings of immunity that can accompany no-vaccine diseases such as Zika virus.

This work is an important contribution to the research behind mosquito and vector vaccination and delaying disease emergence Lipman added.