Exposure to Streptococcus pyogenes (Strep A) that causes mild or no symptoms can trigger the body’s immune response and naturally build protection, potentially solving a nearly 100-year-old mystery of immunity.
New Griffith University research, with the help of clinical scientists from the Murdoch Children’s Research Institute (MCRI), investigated how immunity developed over time as infection rates declined with age, suggesting progressive immune protection. The paper “Subclinical exposure to Streptococcus pyogenes drives the development of long-lived homologous immunity” has been published in Nature Communications.
Strep A is a common bacterium that can cause painful tonsillitis and impetigo in young children and teenagers. If untreated, it can lead to rheumatic fever, rheumatic heart disease and kidney disease, conditions for which First Nations peoples in Australia suffer some of the highest reported rates in the world.
An estimated 10%–20% of children across Australia develop Strep A tonsillitis each year, with some getting the disease multiple times and requiring surgical removal of their tonsils.
By adulthood, most people have developed immunity to Strep A even though most will have had only a few bouts of tonsillitis in their lives.
A long-standing immunity puzzle
Senior author Manisha Pandey, an associate professor at Griffith’s Institute for Biomedicine and Glycomics, said, “How this might happen has never been adequately explained, as there are more than 250 distinct strains of Strep A, and immunity to one strain does not provide protection against the others.”
“To address this question, the team investigated the development of immunity using samples collected through a controlled human infection study conducted by MCRI researchers, who administered a dose of Strep A high enough to cause tonsillitis in most, but not all, participants.
“All participants were treated with antibiotics, regardless.
“Surprisingly, antibodies from the asymptomatic participants not only bound strongly to the exposed strain of bacteria but were able to kill the Strep A germ in a murine model of tonsillitis.”
Silent infections leave a mark
The findings demonstrated that both symptomatic and asymptomatic participants developed robust immune responses to the Strep A strain to which they were exposed.
Dr. Ailin Lepletier said it had been known for many years that multiple strains of Strep A were circulating in the community and that up to 30% of people had Strep A in their throats without getting sick.
“But we didn’t know this may provide immunity to these strains through silent infections, so that by adulthood, we have accumulated antibodies to fight most strains,” she said.
“While a person may not feel sick, their body can still learn how to fight the bacteria and remember it from childhood into adulthood.”
Limits for vaccine design
Professor Michael Good AO said this mechanism of natural immunity may also apply to other common infections.
“While highly intriguing for Strep A, it is unlikely to provide a vaccine strategy, as it would be necessary to vaccinate against each of the 250 strains,” he said.
“The findings highlight the importance of investing in research that addresses conditions disproportionately affecting First Nations peoples,” Dr. Calkin said.
“By improving our understanding of how natural immunity to Strep A develops, this work may contribute to future efforts to prevent rheumatic heart disease and close longstanding health gaps.”
The research team included Griffith University Professor Daniel Kolarich, plus MCRI researchers Associate Professor Joshua Osowicki and Professor Andrew Streer. https://news.griffith.edu.au/2026/08/13/strep-a-immunity-is-possible-without-getting-sick/
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