New Oral Vaccine Demonstrates Strong Defense Against Salmonella Paratyphi A
A recent clinical investigation has revealed that an experimental oral vaccine, CVD 1902, offers substantial protection against infection by Salmonella Paratyphi A, a major contributor to enteric fever worldwide. The study, led by researchers at the University of Oxford, employed a controlled human infection model to assess the vaccine's safety and effectiveness in a group of healthy adult participants.
Enteric fever, commonly caused by Salmonella Typhi and Salmonella Paratyphi, affects millions of people each year, resulting in over 100,000 deaths globally and significant health burdens, especially in resource-limited settings. Notably, around 30% of enteric fever cases are attributed to S. Paratyphi A, for which no licensed vaccine has previously existed.
The phase 2b study was a rigorous, randomized, double-blind, placebo-controlled trial conducted across six sites in the United Kingdom. A total of 72 adult volunteers aged 18 to 55 were enrolled and assigned to receive either two oral doses of the CVD 1902 vaccine or a placebo, administered two weeks apart. Four weeks following the second dose, all participants were intentionally exposed to S. Paratyphi A under closely monitored clinical conditions to evaluate the vaccine's protective capacity.
Results from the trial indicated that within two weeks of exposure, only 21% of those who received the vaccine developed an infection, compared to 75% in the placebo group. These findings translate to a vaccine efficacy rate of 73%, with a confidence interval ranging from 46% to 86%. Importantly, no serious adverse reactions related to the vaccine were reported, and any side effects observed were predominantly mild to moderate in severity, affecting both the vaccine and placebo groups similarly.
This research marks a significant advancement in the fight against paratyphoid fever, a disease that remains a substantial threat in many regions lacking adequate public health infrastructure. While vaccines targeting typhoid fever have been introduced in several countries, the absence of a paratyphoid-specific vaccine has left a gap in preventive strategies against enteric fever. The success of CVD 1902 in providing protection within a controlled setting is a critical step toward closing that gap.
With these positive results, the development of paratyphoid vaccines is advancing, and additional studies are underway to evaluate new bivalent vaccine candidates that combine protection against both typhoid and paratyphoid infections. Such efforts aim to streamline and enhance global enteric fever prevention, particularly in areas where the disease burden is highest.
The study's outcomes not only highlight the safety and efficacy of the CVD 1902 oral vaccine but also demonstrate the utility of controlled human infection models in accelerating vaccine research. This approach allows for the rapid evaluation of candidate vaccines using smaller study populations before larger scale trials commence in endemic settings.
As further research progresses, these findings offer hope for the future introduction of effective vaccines against S. Paratyphi A on a global scale, potentially reducing the incidence of enteric fever and improving health outcomes in vulnerable communities.