At MIT's Koch Institute, researchers have engineered a polio vaccine that could finally close one of the last gaps in the world's push toward complete eradication—by making an injection as effective at blocking viral spread as the riskier oral alternative.
The challenge has long been a frustrating paradox. The injectable polio vaccine (IPV), used in the United States and many wealthy nations, protects people from getting sick. But it doesn't stop them from catching the virus and shedding it in their stool, potentially spreading infection through contaminated water or food to unvaccinated people. The oral polio vaccine (OPV) is far better at this—it triggers mucosal immunity in the gut, where the virus first takes hold. But the OPV comes with a small but real risk: in rare cases, the weakened virus can mutate back into an infectious form, and countries have largely abandoned it for this reason.
Now, a team led by Ana Jaklenec and Robert Langer has cracked the problem by modifying the injectable vaccine with a nanoparticle-based adjuvant that steers immune cells directly to the mucosal lining of the intestine. In rat studies, the vaccine produced a 20-fold increase in the type of antibodies needed for mucosal immunity compared to standard IPV. The breakthrough, published in Science Advances with MIT postdoc Behnaz Eshaghi as lead author, combines the safety of the injection with the transmission-blocking power of the oral dose.
"People who are vaccinated with the injectable vaccine are not getting sick, but they may be helping the virus circulate," Jaklenec explains. "Mucosal immunity could help lower that shedding and ideally eliminate it."
The adjuvant itself—a derivative of vitamin A called Am80—was already known to work, but it required multiple daily injections, impractical for most vaccination campaigns. The MIT researchers solved this by encasing Am80 in lipid nanoparticles that release the adjuvant slowly over several days, eliminating the need for repeated shots. Among several nanoparticle types tested, the lipid version performed best, allowing a single injection to deliver the same effect.
Why this matters now: Polio is on the verge of eradication. Cases are rare globally, endemic only in Pakistan and Afghanistan, yet the virus persists precisely because vaccination rates remain imperfect and vaccinated people can still transmit it. The virus is frequently detected in wastewater even in heavily vaccinated countries. Meanwhile, the oral vaccine carries enough risk that many nations have stopped using it, despite its mucosal immunity advantage. A vaccine that combines the safety profile of IPV with OPV's transmission-blocking power would remove a major barrier to the final push.
The MIT team collaborated with Harvard Medical School researchers on this work, building on Harvard's earlier discovery of Am80's potential as a vaccine adjuvant. The innovation speaks to a broader shift in vaccine science: as traditional targets disappear, researchers are engineering solutions tailored to the last-mile challenges of global health—where perfecting what we already have can matter more than inventing something new.
Human trials would follow animal testing, but the pathway forward is clear. A single injection that stops both illness and spread could be the final tool needed to consign polio, once among humanity's most feared diseases, to history.