A vaccine for one of the planet’s most prevalent and recalcitrant causes of severe bacterial diarrhea has shown promising results in a rigorous human study. The experimental oral vaccine, called WRSs2, was about 89 percent effective in shielding healthy adults from shigellosis, the findings published in the journal The Lancet Infectious Diseases have shown. Shigella is highly transmissible via contaminated food and water, or intercourse, and causes tens of millions of cases globally annually.
The disease is a major contributor to morbidity, stunting and mortality in young children in many low and middle-income settings. It is also a cause of outbreaks in institutionalised groups such as travelers, military personnel, childcare centers and others.
The emergence of multidrug resistant strains has further heightened the problem. The current candidate is a live attenuation ofShigella sonnei, the biogroup strain most commonly encountered in the industrialized world and cases linked to international travel. For phase 2 testing, 108 healthy adults aged 18 to 49 were randomized to receive either one or two doses of vaccine or placebo. 73 volunteers volunteered for a controlled challenge (directly ingesting an exact dose of fully virulent bacteria with medical supervision) approximately four weeks after their last dose. The effects were remarkable.
Of 34 people vaccinated twice, only 3 developed shigellosis while 21 of 26 people who had taken the placebo did. Together with a lower than expected number of severe cases of high temperature and rigours, fewer bacteria were shed by vaccinated subjects with lessen the time helped to stop further infection spreading. The dose was modified during the trial after a few subjects had brief, severe side effects after vaccination.
These withdrew spontaneously and there was no serious adverse effects due to vaccine or mortality. The data is consistent with a two-dose schedule at the modified dose providing good protection with an acceptable balance of risks for healthy adults.
Though, researchers warn more work is needed. Determining the optimum dose for various groups of people, Mostly young children in endemic regions of the world, will be crucial. Extensive testing will be required to validate the protection, proven in the challenge study, on a larger scale and determine the efficacy of the vaccine against other major Shigella species.
Yet, the protection seen so far far surpasses that of previous experimental vaccine candidates. To families and health systems that face ongoing outbreaks, what is proposed here brings a long-standing missing piece of the puzzle: hope of realistic hope that in future, a practical oral vaccine might yield a significant reduction in the burden of a disease that continues to cause suffering.
