Researchers at Stanford University are developing a new way to administer vaccines—without needles. Instead of injections, they are investigating whether a common skin bacterium, Staphylococcus epidermidis, could deliver vaccines through a simple topical cream.
The discovery challenges long-held beliefs about the immune system’s response to skin bacteria. Traditionally, scientists thought these microbes played little role in immunity. But new research shows otherwise.
Unexpected immune reaction
Michael Fischbach, a bioengineering professor at Stanford, and his team found that the body produces a surprisingly strong immune response to S. epidermidis, a normally harmless bacterium living on human skin. The immune system generates high levels of antibodies—defense proteins that fight infections—against it, even without an active infection.
Scientists created a vaccine cream that triggers the same immune response as a shot
Stanford scientists transform ubiquitous skin bacterium into a topical vaccine. pic.twitter.com/hq3sOv06VY— Camus (@newstart_2024) January 16, 2025
That reaction puzzled researchers. Our immune system fights these bacteria even though they are harmless, Fischbach explained. Scientists now believe the response serves as an extra layer of protection. The skin acts as a barrier, but it isn’t perfect. Minor cuts and scratches allow bacteria inside. Antibodies standing guard may prevent infection before it starts.
Unlike traditional vaccines, which trigger an immune response only after an infection begins, this reaction happens before any bacteria invade. That insight opened the door for a new approach to vaccination.
A straightforward experiment on mice
To test their theory, researcher Djenet Bousbaine conducted a straightforward experiment. She swabbed S. epidermidis onto the heads of healthy mice, then monitored their blood for six weeks. The goal was to see if their immune system produced antibodies in response.
The results were striking. Antibody levels increased steadily, reaching concentrations higher than those seen with traditional vaccines—and they remained elevated.
It was as if the mice had been vaccinated, Fischbach said. Their immune system reacted just as strongly as if they had encountered a dangerous pathogen.
Further tests on human blood samples revealed a similar pattern. People naturally carry high levels of antibodies against S. epidermidis, similar to those generated after routine vaccinations.
A step toward painless vaccines
With this knowledge, the researchers set out to turn S. epidermidis into a vaccine platform. They identified a key protein, Aap, which plays a crucial role in triggering the immune response. Aap, a large structure on the bacterial surface, interacts with immune cells that patrol the skin.
Bousbaine then altered the bacterium, replacing part of the Aap protein with a harmless fragment of tetanus toxin. The goal was to see if the immune system would recognize the tetanus fragment and produce protective antibodies.
In a follow-up experiment, mice swabbed with the engineered bacteria developed strong antibody responses against tetanus. When injected with a lethal dose of tetanus toxin, only the mice treated with the modified bacteria survived.
Prevent infections before they even start
This breakthrough suggests that S. epidermidis could serve as a painless, skin-based vaccine delivery system. Beyond tetanus, the approach could be adapted to protect against respiratory diseases such as the flu and COVID-19.
This could prevent infections before they even start, Fischbach said. Unlike current vaccines, which work only after a virus enters the bloodstream, this method could stop pathogens at their entry points, such as the nose and lungs.
Researchers hope their discovery leads to a new generation of vaccines—cheaper, more accessible, and needle-free. While further studies are needed, their findings mark a significant step toward revolutionizing immunization.