Thursday, 8 November 2018

"Increased frequency of travel may act to decrease the chance of a global pandemic"


The high frequency of modern travel has led to concerns about a devastating pandemic since a lethal pathogen strain could spread worldwide quickly.

Many historical pandemics have arisen following pathogen evolution to a more virulent form. However, some pathogen strains invoke immune responses that provide partial cross-immunity against infection with related strains.

Here, we consider a mathematical model of successive outbreaks of two strains: a low virulence strain outbreak followed by a high virulence strain outbreak. Under these circumstances, we investigate the impacts of varying travel rates and cross-immunity on the probability that a major epidemic of the high virulence strain occurs, and the size of that outbreak.

Frequent travel between subpopulations can lead to widespread immunity to the high virulence strain, driven by exposure to the low virulence strain. As a result, major epidemics of the high virulence strain are less likely, and can potentially be smaller, with more connected subpopulations. 

Cross-immunity may be a factor contributing to the absence of a global pandemic as severe as the 1918 influenza pandemic in the century since.

Seems plausible to me. Either we have just been incredibly lucky for the past century, or there is a self-correcting mechanism that reduces the risk of pandemics.


Derek said...

It's probably a balance between increased travel, leading to more transmission opportunities; new vaccines, improved hygiene and better health education, leading to better prevention; and new drugs, leading to more cures or at least a reduction in infectiousness.

The last big outbreak with pandemic potential was the HIV one. It was prevented from becoming a pandemic in the early 1990s by a combination of public health initiatives, including education and various public health measures such as needle exchanges and contact tracing. By the early 2000s drugs had been developed which, although unable to cure the disease, were able to make it almost impossible to pass on as long as people took the drugs.

The situation nowadays is that HIV is mostly transmitted by people who don't know they are infected. Contact tracing is effective enough to keep the transmission rate low but not effective enough to wipe it out.

But the bottom line is that it isn't just luck that prevents pandemics. There are a lot of people working hard to stop them.

Mark Wadsworth said...

D, true. Also HIV has become less virulent over the years.

Graeme said...

So the flu of 1919 was catastrophic, hitting a world weakened by famine and war for 4 years. Every so often we get a flu virus more virulent than the recent ones but the swine flu of 2009? Wasn't that bad really, compared to 1919. Once a virus gets to the developed world nowadays, it reaches immune systems that it cannot overwhelm. That's my theory

Mark Wadsworth said...

G, that's the same theory as proposed in the article.