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100 years later, flu epidemic remains a possibility, Stanford physicians say

One hundred years after the 1928 influenza epidemic, flu remains a threat to society today, several Stanford emergency medicine clinicians explain.

The year is 1918. Millions around the world are dying from a new flu strain. Oddly, young, healthy people seem to be at particular risk. The world is at war, but before the disease epidemic is over, more will die from the flu than on the battlefield. The life expectancy in the United States will drop ten years, from 55 to 45.

This year marks centenary of the 1918 influenza pandemic, the worst in modern history. Estimates place the total worldwide death toll above 50 million people.

But that was 100 years ago, and science and technology have advanced. In the 1930s, scientists proved the flu was caused by a virus, not bacteria, and in 1960, the U.S. Public Health Service began recommending annual vaccinations for people at high risk of serious flu complications. In 2005, the genome of the 1918 virus was fully sequenced.

So it will never, ever happen again. We are safe now, yes?

Well, not really.

The virus that caused the pandemic continued to circulate seasonally for 38 years, and in 2009, a distant cousin of the 1918 flu emerged. I spoke recently with Milana Boukhman, MD, and Colin Bucks, MD, of Stanford Emergency Medicine about the impact of the 1918 epidemic and the likelihood of a pandemic on a similar scale.

As a specialist in biosecurity and bioterrorism preparedness and response, as well as an emergency medicine physician, Boukhman has toured labs around the world where bioweapons were once developed. And yet, she noted, “in many ways, Mother Nature is the worst bioterrorist of all. The 1918 strain was deadly, but keep in mind this was before aviation, urbanization, and global travel.” If the same circumstances arose today, Boukhman pointed out, the consequences would be even greater:

There are forces at work that increase the threat of a natural pandemic. You have globalization and far more people traveling. The airplane is now a ‘super vector,’ transmitting disease from population to population and across continents. Urbanization increases risk as well, especially if you have many people confined to a small area with little to no access to safe food or water. Transmission risks increase.

Yes, but we have vaccines, I prompt.

“It takes many months to develop and produce vaccines," she responded. "Currently the influenza vaccine production process most commonly involves growing virus in eggs. The manufacturing process is relatively slow, and then it also takes time to distribute the vaccine. Currently, seasonal influenza vaccines are made based on an estimation of which influenza strains are most likely to circulate in the population, but this is by definition an estimate, and therefore is not 100 percent predictive."

Bucks, who was part of the team to travel to Africa during the Ebola crisis, explained why the flu was so deadly in 1918. “That particular strain caused a hyper-response from the immune system, inflaming the lungs and the kidneys. The younger you were and the stronger your immune system, the more readily it reacted to the disease. In fighting the strain, the body ended up killing itself. That is why so many young people were impacted.”

When scientists create models of possible pandemics, they often look at bird migration patterns and swine populations, because virus mutations often start in birds before jumping from bird to pig, and then from pig to human, Bucks said.

Viruses that are very different from anything that a population has previously been exposed to are particularly problematic, because immune systems are caught unprepared.

A flu strain that is both highly transmissible and also the result of significant reassortment of gene segments spells trouble.

Just how much trouble is a matter of some conjecture. But if nothing else, the thought alone is motivation to line up for your flu shot this fall.

Photo of Adrene Garabedian receiving a flu shot from Mo Cao by Perla Leal

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