Shigellosis vaccine protects against bacteria becoming increasingly resistant to antibiotics
Scientists have taken a step toward developing an effective vaccine against shigellosis, the infection caused by Shigella bacteria.
In a small clinical trial, two oral doses of a vaccine called WRSs2 protected participants against shigellosisresearchers reported June 30 in Lancet infectious diseases. Protection “is higher than has generally been reported for previous years.” Shigella vaccine studies,” says study co-author Nadine Rouphael, a vaccinologist at Emory University in Atlanta.
This experimental vaccine has “very encouraging results,” says molecular microbiologist Shangxin Yang, who was not involved in the work. But he says the vaccine is still a long way from being approved by vaccine regulators because a large clinical trial to confirm effectiveness would take three to six years. There is currently no approved vaccine against shigellosis.
Shigellosis is spread when small amounts of fecal matter contaminate food, water, or surfaces, and it can also be spread through sexual contact. In the United States, the bacteria causes approximately 450,000 infections each year. about 242,000 of these infections are resistant at least one antimicrobial drug. Worldwide, the bacteria causes at least 80 million infections each year; symptoms include diarrhea, fever, nausea and abdominal cramps. It is most dangerous for children under 5 years old and can be fatal.
The vaccine that Rouphael is testing contains a weakened strain of Shigella species S. Sonnei. In an earlier trial, data showed that the oral vaccine had weakened properties. S. Sonnei East safe and well tolerated. The vaccine needs to “work in the gut, where the infection starts, and it needs to be strong enough to protect but gentle enough not to cause too many stomach and intestinal symptoms,” she says.
In the new trial, the team recruited 108 U.S. adults ages 18 to 49 who had little pre-existing immunity to S. Sonnei and gave many of them up to two doses of vaccine. Two people developed symptoms of severe shigellosis and did not continue. Scientists gave a large group of remaining participants two doses of 500,000 weakened S. Sonnei bacteria – half the previous dose – 28 days apart. Another group received a placebo.
Nearly a month later, scientists tested the vaccine’s effectiveness in a closely monitored hospital environment, where participants received a live, full-strength oral dose of approximately 1,500 doses. S. Sonnei bacteria. Only 3 of 34 participants who received two doses of the vaccine developed shigellosis, compared to 21 of 26 participants who received the placebo. Additionally, only one, or 3 percent of the vaccinated participants developed serious symptoms of shigellosis such as high fever or excessive diarrhea, while 18, or 69 percent of the placebo participants had similar symptoms.
Epidemiologist David Sack of the Johns Hopkins Bloomberg School of Public Health says it could be difficult to find the right oral dose of vaccine for the general population because different groups might respond differently to it.
Additionally, the vaccine tested for the dominant strain Shigella species in the United States, but worldwide, the dominant species is S. flexneri. Because the vaccine was tested in adults and in the world’s less common species, it’s unclear whether it would work in young children in low- and middle-income countries, who bear the greatest disease burden, said Yang, of the UCLA School of Medicine.
Sack was part of a team working on a intramuscular vaccine which reported a 30 percent reduction in shigellosis. Other injectable vaccines are also promising and could probably be safer, he said.
Rouphael’s team plans to continue testing WRSs2, and she says she would like to test it with populations “who need it most, particularly young children in places where Shigella is common.