Minimal Altruism Needed to Halt Epidemic Spread

Even people who are only barely altruistic still choose to self-isolate when infected, suggesting it may be a natural survival strategy.

Published on Feb. 24, 2026

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A new study led by researchers at the University of Warwick has found that even people with only a small amount of altruism would still choose to self-isolate when infected, which can help slow the spread of infectious diseases. The study used mathematical modeling and game theory to explore how individuals make decisions during an epidemic based on factors like infection status, concern for others, outbreak size, and transmission rates.

Why it matters

The findings provide a theoretical foundation for understanding how and when public health messaging appealing to empathy and altruism can be effective in encouraging people to isolate and reduce disease transmission. The researchers say the low level of altruism required suggests this response may reflect an evolved strategy in social animals to protect themselves and their relatives.

The details

The study found that two different epidemic outcomes can emerge - one where infected individuals are altruistic enough to aggressively self-isolate, suppressing the disease long-term, and another where infected individuals choose not to isolate, leading to the disease spreading until population immunity builds up. The researchers say only a small amount of concern from infected individuals is enough to allow for indefinite suppression as an alternative to herd immunity, potentially resulting in far fewer infections, deaths, and social disruption.

  • The study was published on February 24, 2026 in the Proceedings of the National Academy of Sciences.

The players

University of Warwick

The university where the lead researchers on this study are based.

Matthew Turner

Professor at the University of Warwick and senior author of the study.

Simon Schnyder

Co-author of the study and Project Assistant Professor at the University of Tokyo.

Mark Lynch

PhD student at the University of Warwick and co-author of the study.

Ryoichi Yamamoto

Professor at Kyoto University and co-author of the study.

John Molina

Professor at Kyoto University and co-author of the study.

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What they’re saying

“You don't have to care deeply about others to help stop the spread of an infectious disease. Even a tiny amount of concern for others can be enough to change the course of an epidemic.”

— Matthew Turner, Professor, University of Warwick (Mirage News)

“In game theory, we call these outcomes Nash equilibria - stable states that populations settle into because individuals cannot improve their situation by changing their behaviour alone.”

— Simon Schnyder, Project Assistant Professor, University of Tokyo (Mirage News)

“What separates these two equilibria is how altruistic people are - and remarkably, the threshold needed to stabilise disease suppression can be extremely low.”

— Mark Lynch, PhD student, University of Warwick (Mirage News)

“We can strengthen public cooperation further by communicating early and making isolation both morally and rationally compelling. It is crucial to understand that the required altruism greatly increases with the size of the outbreak: the more people already infected, the harder it becomes to preserve indefinite suppression.”

— Ryoichi Yamamoto, Professor, Kyoto University (Mirage News)

“Policy doesn't need to invent new behaviour. Messages like 'stay home to protect granny' tapped into a natural altruistic tendency.”

— John Molina, Professor, Kyoto University (Mirage News)

The takeaway

This study provides important insights for public health policy, showing that even a small amount of altruism among individuals can be enough to significantly slow the spread of an infectious disease through self-isolation. The findings suggest public messaging that appeals to this natural altruistic tendency can be an effective way to encourage protective behaviors during an epidemic.