Avian Influenza and Influenza Pandemics

Editorials

Avian influenza and influenza pandemics Stefano Lazzari1 & Klaus Stöhr2

Well before the 31 influenza outbreaks are growing concerns that if H5N1 were Vaccination and antiviral drugs can recorded since the first pandemic was to become transmissible in humans, the reduce influenza morbidity and mortal- described in 1580, pandemic-like events heavy toll of the 1918–19 “Spanish flu” ity, but their initial availability will be were reported as early as the fifth century pandemic could be repeated (3). limited and the large-scale production of BC by the Greek physician Hippocrates. Most experts believe that future a new pandemic vaccine would take In the last century, the “Spanish flu” influenza pandemics are inevitable and several months. If a new pandemic pandemic of 1918–19 killed 20–40 may be imminent (4). Nobody can be strain is detected early enough, selected million people, while the “Asian flu” sure when a pandemic will happen, how public health interventions (including pandemic in 1957 and “Hong Kong flu” quickly it will spread, and what mor- infection control and isolation of patients) in 1968 each caused an estimated 1–4 bidity, mortality and economic impact could slow its initial spread, thus allowing million deaths. it will cause. Forecasting models predict more time for response measures to be Pandemics originate with the emer- a major disease burden, with 25–30% of implemented. National pandemic pre- gence of a new subtype of influenza virus the population falling ill and potentially paredness plans are being discussed in able to cause disease, replicate in humans, enormous economic costs worldwide, several countries though few have been and spread efficiently from one person especially in the poorest countries where finalized (5). to another. An avian influenza virus can resources for surveillance and health care Strengthening and expanding control improve its transmissibility in humans by are limited and population health and activities for annual influenza epidemics adaptive mutation or genetic reassort- nutritional status are poor. that account for significant morbidity, ment (the mixing of animal and human A comprehensive public health mortality and economic loss. The WHO influenza viruses). Recent studies confirm approach to influenza pandemics must Global Influenza Surveillance Network that the 1918–19 pandemic probably include at least four key activity areas: regularly monitors the variation of the originated from the reassortment of avian Limiting the circulation of avian influenza virus, issues recommendations and human viruses (1). and other animal influenza viruses. The on influenza vaccine composition, and Reports of human infections main strategy for preventing the emergence provides prototype vaccine viruses to and deaths caused by avian influenza of a pandemic virus is to reduce the vaccine manufacturers. Only about 300 virus A(H5N1) in Hong Kong Special opportunities for human exposure to million doses of vaccine are distributed per Administrative Region in 1997 (2) and animal viruses with demonstrated human year, however, and vaccination coverage 2003, and in Viet Nam and Thailand in pathogenicity. Human infections with could be improved (6). The World Health 2004 are stark reminders of the threat avian influenza viruses and mutations Assembly in May 2003 set targets for of pandemic influenza. Outbreaks of leading to efficient human-to-human vaccination coverage of elderly people and avian influenza are increasingly frequent, transmission are both rare events. How- people with underlying diseases of 50% probably as a result of intensive agricul- ever, large outbreaks in poultry magnify by 2006 and 75% by 2010 (resolution tural practices, high virus transmissibility the possibility of human infection. Con- WHA56/19). Increasing global vaccine and the presence of natural reservoirs certed efforts are required to eliminate the production capabilities and working in migratory birds. The ability of three main source of the virus, including the towards these targets would also ensure of the 15 known subtypes of avian mass culling of infected animals, poultry a broader and more equitable access to influenza viruses (H5N1, H7N7 and vaccination, surveillance and the con- pandemic vaccines. H9N2) occasionally to infect human sistent application of infection-control Influenza pandemics are natural beings makes them one of the most measures in people who are exposed. events. However, the burden of disease likely candidates to become the next Improving early warning. Early they cause and their economic impact pandemic virus. detection and isolation are essential for could be greatly reduced by the ap- The current influenza outbreaks in ensuring a rapid response to a pandemic propriate use of vaccines, antiviral poultry are unprecedented in their scale, influenza strain. The current global influ- drugs and public health interventions. geographical spread and adverse economic enza surveillance system was designed to Strengthening influenza surveillance, effects among affected populations. monitor genetic variations in order to up- developing pandemic preparedness Containment will require the mobiliza- date seasonal influenza vaccines; it now plans, improving control of avian influ- tion of significant resources over several needs to be strengthened to allow for the enza, and increasing coverage of annual months, leading to continued exposure of early detection and characterization of a influenza vaccination are the corner- many individuals to H5N1. In addition, new pandemic virus and the collection of stones of a safer world. O resistance in current strains to one of the clinical and epidemiological information. two classes of available antiviral drugs has Strengthening pandemic preparedness References been demonstrated in vitro. Because of and response capacities. An influenza Web version only, available at: http:// its high pathogenicity in humans, there pandemic is a major health emergency. www.who.int/bulletin

1 Coordinator, Risk Containment, Mapping and Drug Resistance, Communicable Diseases Surveillance and Response, World Health Organization, 1211 Geneva 27, Switzerland (email: [email protected]). Correspondence should be sent to this author. 2 Project Leader, Global Influenza Programme, Communicable Diseases Surveillance and Response, World Health Organization, Geneva, Switzerland. Ref. No. 04-012641

242 Bulletin of the World Health Organization | April 2004, 82 (4) Editorials

1. Gamblin SJ, Haire LF, Russell RJ, Stevens DJ, Xiao B, Ha Y, et al. The structure and receptor- binding properties of the 1918 influenza hemagglutinin. Science 2004;303:1838-42 (originally published in Science Express online 5 February 2004 [DOI: 10.1126/science.1093155]). 2. Nicholson KG, Wood JM, Zambon M. Influenza. Lancet 2003;362:1733-45. 3. Katz JM. The impact of avian influenza viruses on public health. Avian Diseases 2003;47:914-20. 4. Webby JR, Webster RG. Are we ready for pandemic influenza? Science 2003;302:1519-22. 5. Canadian pandemic influenza plan. Ottawa: Health Canada; 2004. Available from: URL: http://www.hc-sc.gc.ca/pphb-dgspsp/cpip- pclcpi/. 6. Carrat F, Valleron AJ. Influenza mortality among the elderly in France, 1980–90: how many deaths may have been avoided through vaccination? Journal of Epidemiology and Community Health 1995;49:419-25.

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