October 15, 2017
Ralph Baric, PhD
Professor of epidemiology
Professor of microbiology and immunology, UNC School of Medicine
We’re well-prepared for early diagnosis and detection. Some of the new technologies can identify new pathogens within two weeks, assuming the samples are made available and not occurring in a country that does not want to communicate openly about an outbreak.
Also, new methodologies are available to generate candidate vaccines relatively rapidly. In the 2009 outbreak of H1N1 flu, for example, the vaccine strains were developed in three or four days, and we had seed stocks within a week. We can have very rapid movement from identification to candidate vaccines for a population.
Where we’re not prepared is in demonstrating that the vaccines work and getting them into sufficient concentrations for distribution to the general public, first at a national level and then at a global level, which is even more challenging. The most advanced countries can make experimental vaccines and test them within one or two months. However, 90 percent of the world wouldn’t receive that vaccine for several months, if at all.
We also don’t have drugs on a shelf that can be used to treat outbreaks. We need to develop broad-based drugs that attack many members in a virus family. The good news is that some pharmaceutical companies are interested in developing these kinds of drugs, but this is not going to happen overnight.
Q: If something as virulent as 1918 flu appeared today, how fast would it spread, and how long would a vaccine take?
A: 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.
Q: What virus families are most likely to cause a catastrophic outbreak?
A: 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.
Q: What could harden our defenses against future outbreaks?
A: 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.
Carolina Public Health is a publication of the University of North Carolina at Chapel Hill Gillings School of Global Public Health. To view previous issues, please visit sph.unc.edu/cph.