Researchers at Washington University School of Medicine in St. Louis found that a vaccine given to pregnant mice protected their newborn pups from a severe bloodstream infection caused by Klebsiella pneumoniae, a dangerous bacterium that kills thousands of infants in low- and middle-income countries each year and is the leading killer of children globally.
Such infections can be difficult to treat due to the bacterium's growing resistance to antibiotics and there is currently no vaccine available to prevent infection. The study, published Oct. 14 in Science Advances, points to a promising new strategy for protecting vulnerable infants from the drug-resistant superbug by harnessing maternal immunity.
"Klebsiella pneumoniae is a serious threat to newborns who have not yet developed their own immune defenses," said the study's senior author, David A. Rosen, MD, PhD , an associate professor of pediatrics and of molecular microbiology at WashU Medicine. "Our study shows that maternal immunization can effectively bridge that critical window of vulnerability, giving newborns the protection they need right from birth."
Harnessing maternal immunity
K. pneumoniae is a big problem around the world, especially in the hospital where it can cause pneumonia and other infections among adults and children. In low- and middle-income countries, where children often get exposed to the bacterium in their environment, it drives severe bacterial blood infections, known as sepsis. Because K. pneumoniae is increasingly resistant to standard antibiotics, doctors are often left without effective medicines to treat such infections.
The Rosen team collaborated with the lab of Drew Schwartz, MD, PhD , an assistant professor of pediatrics, to model K. pneumoniae sepsis in newborn mice that mimics the infection seen in children and asked if vaccinating a pregnant mouse would prevent infection in pups.
"This study presents the first evidence that giving moms a vaccine could be an effective strategy for protecting their babies against these severe infections."David A. Rosen, MD, PhD, WashU Medicine
Female mice were immunized at the time of mating and then again once or twice during pregnancy. The vaccine targets two of the most dangerous types of K. pneumoniae — known as K1 and K2 — and was developed by Omniose, a St. Louis-based startup. Rosen had previously published findings that show the vaccine is effective in preventing K. pneumoniae infection in adult mice that can progress to life-threatening liver, respiratory tract, bloodstream and other infections.
Two weeks after birth, the young mice were exposed to lethal doses of the bacteria, either the K1 or K2 type. Of the two-week-old mouse pups from unvaccinated mothers, 0% infected with the K1 type and less than 35% with the K2 type survived. In contrast, of the young mice from vaccinated mothers, more than 80% infected with either type survived. Whether the mother received two or three doses of the vaccine did not impact survival.
The researchers drew blood weekly from the young mice starting on their day of birth and continuing up to six weeks of life. They also collected breast milk from lactating mice. They found high concentrations of vaccine-specific antibodies in both the milk of vaccinated mothers and their newborn mice over the course of the study.
"Mice that were never immunized themselves are highly protected from a lethal infection just from the durable antibodies transferred to them from their mother," explained first author Paeton Wantuch, PhD, a staff scientist in the Rosen lab.
The researchers are now testing updated vaccines designed to shield against multiple strains of the superbug found across the globe.
"This study presents the first evidence that giving moms a vaccine could be an effective strategy for protecting their babies against these severe infections," said Rosen. "And it also has established a practical model that we can now use to test therapies and vaccines that will bring us one step closer to human clinical trials with the ultimate goal of impacting global health."
Wantuch PL, Tung J, Robinson LS, Darwech I, Knoot CJ, Harding CM, Schwartz DJ, Rosen DA. Maternal vaccination with capsular polysaccharide bioconjugates protects against murine Klebsiella pneumoniae neonatal sepsis. October 14, 2026. Science Advances. DOI: 10.1126/sciadv.aeh8222
This work was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health (NIH), grant numbers R01AI175038, R01AI195492 and K08AI159384; the Gates Foundation, grant number INV-088225; Washington University Department of Pediatrics. The content is solely the responsibility of the authors and does not necessarily represent the official view of the NIH, the Gates Foundation or other funders.
Competing Interest Statement: Robinson LS, Darwech I, Knoot CJ, Harding CM have a financial stake in Omniose, a for-profit entity developing bioconjugate vaccines using patented technology reflected in the data presented in this and other published manuscripts.
