Tests involving three different kinds of Zika vaccines on rhesus monkeys have produced good immune responses and caused no adverse effects, raising hopes for the development of an effective vaccine for use in humans. None of the vaccinated monkeys developed infection when later challenged with Zika virus. Also, the transfer of antibodies at higher doses from vaccinated monkeys to Zika-naïve mice and monkeys was found to offer “complete protection” when the animals were exposed to Zika virus.
Three vaccine approaches
The results of the study by a team led by Dan H. Barouch from Harvard Medical School, U.S. are to be published on August 5 (Thursday) in the journal Science .
Zika virus strains from both Brazil and Puerto Rico were used for developing the vaccines. The study used three vaccine approaches — a purified killed Zika virus, DNA from the Zika virus woven into a plasmid, and inserting Zika genes into adenoviruses which infect cells and trigger immune responses.
In addition, passive protection was also tested by using antibodies from vaccinated monkeys to protect Zika-naïve mice and monkeys. While all the mice that got the antibodies at a higher dose were completely protected, one of the two monkeys that got the antibodies was completely protected.
The vaccine study using purified killed virus vaccine was conducted on 16 rhesus monkeys. Eight monkeys got the purified killed virus vaccine and the remaining eight did not get a vaccine. Within two weeks of immunisation, all vaccinated animals developed Zika-specific binding and neutralising antibodies. After a booster vaccine was administered at four weeks, the antibody levels increased substantially. When these animals were exposed to Zika virus, they showed “complete protection”.
In another experiment, 12 rhesus monkeys were immunised with either a DNA vaccine or an adenovirus vector-based vaccine. While the monkeys developed antibodies when both the vaccines were administered, the adenovirus vector-based vaccine provoked a broader and a more potent antibody response. Both the vaccines conferred complete protection when the vaccinated monkeys were exposed to Zika virus four weeks after vaccination.
