Seasonal influenza is a unique public health conundrum: its epidemics are annual, yet even with the wealth of epidemiologic data now collected on it, predicting its activity and severity still remains a significant challenge. Recent modelling suggests that the global burden of influenza is worse than previously thought, accounting for up to 600 000 deaths annually.
Australia was particularly hard-hit by influenza in 2017. The May to October flu season had the highest levels of activity since the 2009 pandemic, with approximately 2.5 times as many laboratory-confirmed cases recorded in 2017 as in 2016. This increase may have been partially due to increased use of new, rapid testing technology which is now available.
Several factors contributed to last year’s difficult flu season, the most notable being the longer peak season, low vaccine effectiveness, and low vaccine uptake. Specifically, the peak season lasted longer than usual: typically, the peak is, at most, four weeks, but in 2017, it lasted for six weeks. The effectiveness of the 2017 vaccine in preventing a general practitioner visit was estimated to be low overall at 33% and even lower (16%) in preventing hospitalisation. The overall effectiveness was weighted lower due to the relatively poor effectiveness against the predominant circulating strain A/H3N2.
Mortality rates were consistent with recent years despite an increased number of deaths reported due to the overall greater number of infections. Also, despite higher hospital admissions due to influenza, the average clinical severity was lower than in the past based on the proportion of those affected who were admitted to the intensive care unit. More than half of the confirmed cases were from an influenza A/H3N2 strain. Deaths were concentrated among the elderly population, which is to be expected in H3N2-dominant years.
Australia’s 2017 flu season also foreshadowed that of the Northern Hemisphere, which had an early start and widespread activity as well. Overall U.S. vaccine effectiveness, at 36% according to the Centers for Disease Control and Prevention (CDC), was not much better than that of Australia, and high numbers of hospitalizations were experienced among seniors as well as deaths among children.
The World Health Organization (WHO) holds technical consultation meetings twice a year – in February/March for the Northern Hemisphere and in September for the Southern, to recommend virus strains for inclusion in vaccines for their upcoming seasons. In September 2017, for the trivalent vaccines, WHO recommended including a new A/H3N2 strain, replacing the Victoria lineage B strain with Yamagata lineage virus, and retaining the H1N1 strain. For the quadrivalent influenza vaccines (QIV), which are used in Australia for all under age 65, WHO recommended keeping the Victoria lineage B strain.
In many ways, choosing components of the seasonal flu vaccine is very difficult and complex. Researchers can assess and anticipate which viruses might predominate and how they might vary, but there’s no real telling until early surveillance data becomes available to determine the actual types and strains circulating for the current year.
Starting this flu season, two higher-immunogenicity trivalent vaccines (Fluzone® High-Dose and FLUAD) are being recommended for those age 65 and older. These vaccines contain larger amounts of antigen or an adjuvant to make the recipient’s immune response more effective. There is growing evidence that these vaccines do indeed provide the elderly with superior protection compared with standard trivalent vaccines. The trivalent vaccines are provided free of charge to all Australians age 65 and older. Many Australians have access to free flu shots under the National Immunisation Program.
At this point, even though flu season is just beginning in Australia (in the tropical North, flu is present year round), it’s too early to tell what the season might have in store. According to BlueDot, a data analytics firm based in Toronto, Canada which studies how infectious diseases disperse worldwide through analysis of big data, there have been more influenza notifications than in prior years at this time of year, although this could be the effect of increased testing. Recent surveillance data shows roughly equal incidence thus far of influenza types A and B. Of type A, approximately 60% is H1N1 and 40% H3N2. However, this early in the season no specific conclusions can be drawn. The demand for the vaccine is also up, which is favorable, but it is also leading to vaccine shortages. Government agencies are responding by working to secure additional sources of vaccine to meet the demand.
Developing strategies to fight both seasonal and pandemic flu requires a concerted global effort. Fortunately efforts are already under way: Bill Gates, in a May 31, 2018 column in the New England Journal of Medicine, cited several research initiatives that The Bill and Melinda Gates foundation is partnering with and funding, including a Grand Challenge to accelerate the development of a universal flu vaccine.
Knowledge of an influenza season’s potential severity, either in advance or at onset of the season, would help insurance companies improve their mortality modelling regarding seasonal mortality variation due to influenza directly or indirectly from its complications. Also important to consider is that age is the most significant risk factor for influenza mortality: more than 90% of all deaths in recent decades have occurred in individuals age 65 and older.
- 2017 Influenza Season in Australia, Australian Government, Department of Health, Information Brief. Updated 22 November 2017.
- BlueDot- https://bluedot.global/ (direct communication and consultation)
- Gates B. Shattuck Lecture: Innovation for Pandemics. N Engl J Med. 31 May 2018: 378(22); 2057-60.
- Ma H, Khan K. Seasonal Influenza and Mortality. ReFlections. 20 January 2018: 43; 11-9
- Iuliano AD et al., Estimates of global seasonal influenza-associated respiratory mortality: a modelling study. The Lancet. March 2018: 391(10127); 1285-1300.
Daniel D. Zimmerman, M.D., VP and Medical Director, Reinsurance Group of America (RGA,) is a member of the Global Support Team where he is responsible for case consultation, product development, internal and external education, client support, and representation to key industry professional organizations. He has held leadership positions with the American Council of Life Insurers (ACLI) and participated in program committees of the American Academy of Insurance Medicine (AAIM). Dr. Zimmerman is also the assistant managing director for the RGA-sponsored, Longer Life Foundation (www.longerlife.org).
Dr. Zimmerman joined RGA in 2014 after previous career experience in clinical medicine and serving as a medical director for Northwestern Mutual in Milwaukee, Wisconsin, USA.
Dr. Zimmerman’s educational background includes a Bachelor of Science degree in molecular biology and medical microbiology and a Medical Doctorate from the University of Wisconsin – Madison, Madison, Wisconsin, USA. He completed training in both internal medicine and pediatrics at the University of Minnesota – Minneapolis, Minnesota, USA. He maintains board certification by the American Board of Internal Medicine and American Board of Pediatrics as well as the American Board of Insurance Medicine.
Professional interests of Dr. Zimmerman include infectious diseases and their global impact on mortality and morbidity, assessing long-term risk in juveniles, public speaking and education, and protecting the ability of insurers to utilize all medical information in the course of underwriting. He also enjoys research and writing and has contributed several articles to the Journal of Insurance Medicine.