WHO’s Assessments Over Time
The purpose of this page is to gather WHO’s assessments of pandemic threat over time, from 2003 on, to review for changes in tone and focus. No one knew in 1997 what we know now about H5N1, and we’ll know even more in months and years to come. Still, changes in language tone and focus might bring more clarity and understanding to a changing situation. But note that the language Monitoring of the evolving situation, coordinated by WHO, has produced many signs that a pandemic may be imminent. Jan 05 and Recent experiences with highly pathogenic H5N1 avian influenza have given the world its first advance warning that another influenza pandemic may be imminent. March 06 are very similar.
The WHO Media Centre Archive is here.
Overall Pandemic Threat
“Influenza is a global threat,” says WHO’s Director General Dr Gro Harlem Brundtland. “It already kills up to a million people each year, and sooner or later it will ignite a pandemic. We can meet this challenge with a strong global surveillance system and a robust health infrastructure, or we will suffer the consequences. Today, we are not ready for the next influenza pandemic. Preparedness has to start now. The situation is urgent.”
A(H5N1) was first seen in humans in 1997 when an outbreak of 18 cases caused six deaths in Hong Kong SAR. Until then, this virus was seen only in birds including chickens and ducks. A(H5N1) is not dangerous for ducks, but causes high mortality in chickens. Following confirmation of the initial case, in a two-year-old child in August 1997, an investigation was launched and surveillance was increased. In December 1997, all chickens, which were thought to be the source of this outbreak of influenza in humans, were slaughtered in Hong Kong SAR. No further cases of this disease was reported in humans. Since then, authorities have maintained intensive surveillance of influenza in human and birds in Hong Kong SAR.
Highly pathogenic avian influenza is a threat to public health because, if it circulates long enough in humans and farm animals, there is an increased risk that it may evolve into a pandemic influenza strain which could cause disease worldwide. In addition, avian influenza is an economic disaster for the poultry industry as well as small poultry farmers.
In the past, pandemics have announced themselves with a sudden explosion of cases which took the world by surprise. This time, we have been given a clear warning. During 2004, large parts of Asia experienced unprecedented outbreaks of highly pathogenic avian influenza, caused by the H5N1 virus, in poultry. The virus crossed the species barrier to infect humans, with a high rate of mortality. Monitoring of the evolving situation, coordinated by WHO, has produced many signs that a pandemic may be imminent. This time, the world has an opportunity to defend itself against a virus with pandemic potential before it strikes.
This new plan addresses the possibility of a prolonged existence of an influenza virus of pandemic potential, such as the H5N1 influenza virus subtype in poultry flocks in Asia, which persisted from 2003 onwards.
It also makes provision for the possibility of simultaneous occurrence of events with pandemic potential with different threat levels in different countries, as was the case in 2004 with poultry outbreaks of H7N3 in Canada and H5N1in Asia. The phases of increasing public health risk associated with the emergence of a new influenza virus subtype that may pose a pandemic threat have been redefined, actions for national authorities are recommended, and measures to be taken by WHO during each phase outlined.
Redefinition of the phases was needed to address the public health risks of influenza infection in animals, link phase changes more directly with changes in public health response, and focus on early events during a “pandemic alert” period when rapid, coordinated global and national actions might help to possibly contain or delay the spread of a new human influenza strain. Even if not successful in containing spread, this approach should gain time to develop vaccines against the new strain, and to implement other pandemic preparedness measures that had been planned in advance. Success will depend on several factors, including surveillance to provide global early warning of human infections with new influenza subtypes. The new phases and the overarching public health goals for each phase are summarized on page 2.
The distinction between phase 3, phase 4 and phase 5 is based on an assessment of the risk of a pandemic. Various factors and their relative importance according to current scientific knowledge may be considered. Factors may include rate of transmission, geographical location and spread, severity of illness, presence of genes from human strains (if derived from an animal strain), and/or other scientific parameters.
This latest outbreak confirms that no country is immune to H5N1. Every country is at risk. Every country must prepare.
If the H5N1 virus changes to allow it to pass easily from person to person, and it goes unchecked, this could trigger an influenza pandemic. H5N1 is spreading rapidly across the world. All countries must take measures to protect human health against avian flu, and prepare for a pandemic.
Recent experiences with highly pathogenic H5N1 avian influenza have given the world its first advance warning that another influenza pandemic may be imminent. Given the serious consequences of past pandemics, this advance warning has stimulated a search for ways to prevent such an event from occurring.
At present, there is no clear evidence that shows that higher dosages than the approved ones will be more effective for patients with H5N1. However, because the optimal dosage has not been resolved by clinical trials, and because H5N1 infections continue to have a high mortality rate, prospective studies are needed urgently to determine optimal dosing and duration of treatment for H5N1. It is possible that severely ill patients might benefit from longer duration of therapy (e.g. 7–10 days) or perhaps higher doses (e.g. 300mg/day), but prospective studies are required.
In terms of safety and adverse effects, evidence from the trials in ordinary influenza shows that although oseltamivir is generally well tolerated, gastrointestinal side effects in particular may increase with increasing doses, particularly above 300mg/day.
There are no adequate data on the use of oseltamivir in pregnant women. The animal toxicology studies do not indicate direct or indirect harmful effects with respect to pregnancy or fetal development. Decisions to use oseltamivir in pregnant women should be made on a case by case basis where the potential benefit to the mother justifies the potential risk to the fetus.