Are we prepared for the next superbug outbreak?
With federal health officials saying that this year’s flu season is now more intense than any since the 2009 swine flu pandemic and still getting worse, we had some questions for researcher Ralph Baric. Baric, whose research specializes in coronaviruses and diarrheal diseases, has appointments in the epidemiology department of the Gillings School of Global Public Health and in the microbiology and immunology department of the School of Medicine.
If something as virulent as 1918 flu appeared today, how fast would it spread, and how long would a vaccine take?
The 1918 flu had about a 30 percent attack rate and a mortality rate of about 2 percent of the world’s population. If we had an analogous outbreak now, given the 7.5 billion people on the planet, we would have about 150 million deaths.
While our public health infrastructure and response rates are better in most countries than in 1918, the world’s population is much, much more mobile. Any flu with heightened attack and mortality rates would spread much more quickly and broadly than in 1918. Because the incubation period could be as much as seven days, victims won’t show symptoms while they spread it. The virus would get a great head start, and there would be significant time before an effective vaccine could be developed.
What virus families are most likely to cause a catastrophic outbreak?
Flu is highest on the list. Only three flu strains have circulated in human populations—H1, H2 and H3—but there are 17 different hemagglutinin genes, so no one has any resistance to the other ones. The more lethal known flu strains are H5N1, which has about a 50 percent mortality rate, and H7N9, with 30 percent mortality. Even if those rates decrease a bit due to higher transmissibility, you’re still talking about a horrific number of deaths. Think about the state of the world with, say, 25 to 45 percent of the population suddenly gone. How does this affect food supply, water supply, sanitation, energy and other basic necessities? The damage goes well beyond the mortality rate.
Coronaviruses are next on this list. In this century, two highly pathogenic coronaviruses have surfaced—severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS)—with mortality rates of 10 percent to 35 percent. So far, transmission occurs from person to person, and the diseases’ symptoms occur before transmissibility. With really good public health approaches, they can be kept from expanding as quickly as a flu.
Most people would include flaviviruses on this list. These are mosquito-transmitted illnesses such as Chikungunya, West Nile virus and Zika. Also of concern would be Ebola, Marburg, Nipna and Hendra.
The caveat to all of these is that viruses have the capability to evolve quickly in new environmental settings, which means that rapid evolution is a reality. For example, in 2000, no experts would have included coronaviruses on this list, but then SARS and MERS evolved. The human race also presents a great evolutionary environment for viruses, especially in the high-population density of our big cities. Those environments are ripe for the rapid evolution of many viruses, especially flu and coronaviruses. The result could be an explosive, catastrophic outbreak.
What could harden our defenses against future outbreaks?
The number-one defense is public health infrastructure—improved hygiene, improved medical facilities and a health-care environment that delivers care quickly. If many people are without access to health care, they become a giant incubator in which any pathogen can adapt and ready itself to be transmitted. Because of this, large areas in South America, Africa and Asia are particularly vulnerable right now.
We also need to improve basic translational science and know the best targets for developing preventions and treatments. The more we understand the enemy—in this case, viruses—the more we can be in control. We must learn more about the functions of all the viral genes—and the structures and proteins, how they replicate. The more we understand, the more we can target and create drugs for entire families of viruses, rather than reacting to outbreaks one at a time.