Why is it so challenging to increase the number of people who get vaccinated? How does vaccination resistance remain strong even as preventable diseases make a comeback?
According to Dartmouth College, USA, research shows that past problems with vaccines can cause a phenomenon known as hysteresis, creating a negative perception that alters and hardens public resolve therefore causing vaccination resistance. The study explains why it is so hard to increase uptake even when overwhelming evidence indicates that vaccines are safe and beneficial.
The hysteresis cycle to vaccination resistance
A hysteresis loop causes the impact of a force to be observed even after the force itself has been eliminated. This is why unemployment rates can sometimes remain high in a recovering economy, or why physical objects resist returning to their original state after being acted on by an outside force. And, Dartmouth research suggests that this is why the public resists vaccination campaigns for ailments like the common flu.
Feng Fu, an assistant professor of mathematics at Dartmouth College explains: “Given all the benefits of vaccination, it’s been a struggle to understand why vaccination rates can remain stubbornly low.”
“History matters, and we now know that hysteresis is part of the answer.”
The research, published in the journal Proceedings of the Royal Society B, is the first study to demonstrate that hysteresis can impact public health.
“Once people question the safety or effectiveness of a vaccine, it can be very difficult to get them to move beyond those negative associations. Hysteresis is a powerful force that is difficult to break at a societal level.” adds Fu.
Vaccination resistance needs to stop
Low vaccine compliance is a public health issue that can cause the loss of ‘herd immunity’ and lead to the spread of infectious diseases. In parts of Europe and North America, childhood diseases like measles, mumps and pertussis have returned as a result of vaccination resistance .
“This study shows why it is so hard to reverse low or declining vaccine levels,” said Xingru Chen, a graduate student at Dartmouth and the first author of the research paper. “The sheer force of factual, logical arguments around public health issues is just not enough to overcome hysteresis and human behaviour.”
According to the research, the hysteresis loop can be caused by questions related to the risk and effectiveness of vaccines. Negative experiences or perceptions related to vaccination impact the trend of uptake over time, otherwise known to the researchers as a ‘vaccination trajectory’ that gets stuck in the hysteresis loop.
Hysteresis prevents an increase in vaccination levels even after the negative objections have been cleared, making society increasingly vulnerable to disease outbreaks.
“The coverage of measles vaccination has only gradually climbed up, but still remains insufficient, for more than a decade following the infamous MMR vaccination and autism controversy.” Chen concludes.
“Vaccination levels in a population can drop quickly, but, because of hysteresis, the recovery in that same population can take many years.”
By identifying the hysteresis effect in vaccination, the research team hopes that public health officials can design campaigns that increase voluntary vaccination rates, particularly by promoting vaccination as an altruistic behaviour that is desired by moral and social norms.