Pandemic influenza virus strains easily infect humans and spread from person-to-person in an efficient and sustained way. With no immunity to the novel virus and no vaccine to protect against it, what will the United States do?
In a recent Association of Health Care Journalists (AHCJ) webcast, 2 experts discussed the pandemic potential of the most concerning flu epidemic circulating in China, and whether the United States is prepared for this threat.
According to Sonja J. Olsen, PhD, deputy chief, Epidemiology and Prevention Branch, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia, seasonal flu is associated with a significant burden of disease in humans each year. In the United States alone, 9.2 million to 35.6 million cases of flu occur each year, causing 12,000 to 56,000 deaths.
“Understanding seasonal flu is necessary to understanding pandemics,” she said.
Of the 4 types of influenza virus, only types A and B are major human pathogens.
Influenza A viruses are especially problematic, she noted, because they can infect a variety of host species, including waterfowl (their natural reservoir), poultry, humans, and pigs. These viruses can also cross the species barrier, causing illness in another species. The viruses have 8 segmented genes and constantly undergo mutation, Dr. Olsen added. And if influenza A viruses from 2 different species infect the same animal or person, the segmented genome allows the 2 different viruses to mix and create a novel influenza A virus.
“A novel flu virus is a subtype of an influenza virus that is different from influenza viruses currently circulating among humans,” she explained. “Pandemics can occur when a novel influenza virus emerges in the human population.”
Pandemic influenza virus strains also easily infect humans and spread from person-to-person in an efficient and sustained way, said Dr. Olsen. In the event of a flu pandemic arising, the population will have no immunity to the novel virus, and no vaccine will be available to protect against it, she added.
She highlighted avian influenza A H7N9 as having the current greatest potential to cause a pandemic. This virus is circulating in poultry in China and sporadically infecting humans. It has caused 5 annual epidemics of human infections since 2013, said Dr. Olsen, and is associated with severe illness: 90% of infected persons have developed pneumonia, 70% have required intensive care unit admission, and 40% have died.
The viruses involved in the fifth wave are also changing, she added. The number of cases of avian influenza A H7N9 is not only rising in humans but is involving a greater geographic spread. Viral genetic drift has also increased the need for new vaccine development, and a subset of viruses is now highly pathogenic in poultry.
Dr. Olsen shared data from a recent study showing that just 3 amino acid mutations were needed to cause a switch in the specificity of avian influenza A H7N9 for human-type receptors. If these 3 mutations were to arise, they could potentially allow the avian virus to spread among humans with devastating effects. However, no evidence of human-to-human transmission of this virus currently exists, she added, which is encouraging.
Nevertheless, improved detection of this virus is critical, said Dr. Olsen, and risk assessment is important for pandemic preparedness. She highlighted CDC’s Influenza Risk Assessment Tool, developed to assess the potential pandemic risk posed by influenza A viruses that currently circulate in animals but not in humans.
According to Michael Osterholm, PhD, MPH, director, Center for Infectious Disease Research and Policy at the University of Minnesota, Minneapolis, another flu pandemic “is going to happen.”
But while this threat is inevitable, how ready are we in the United States for the next pandemic? “The bottom line message is—we’re not,” he emphasized. “We’re not prepared for another 1918-like pandemic.”
Although influenza vaccines will have some impact in protecting the population during a pandemic, Dr. Osterholm stressed that, on a global basis, this effect will be minimal.
Discussing why flu vaccines so often fail, he explained that many factors beyond antigenic match affect the level of protection that vaccines provide. These factors include when during the flu season a person receives a flu vaccine, whether they have previously received a flu vaccine, and which vaccine they received.
“We will have major challenges with the next flu pandemic without better vaccines for the world,” Dr. Osterholm said. Estimating the cost to bring forward a new flu vaccine at more than $1 billion, he highlighted the need for improved vaccines as an international priority. Achieving this will require major commitment and investment, he concluded.
Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.