Influenza A(H1N1) 2009 pandemic - 20 July 2009. ECDC Interim Risk Assessment (Excerpts, edited)

[Giuseppe]

Influenza A(H1N1) 2009 pandemic - 20 July 2009. ECDC Interim Risk Assessment (Excerpts, edited)

ECDC INTERIM RISK ASSESSMENT

Influenza A(H1N1) 2009 pandemic - 20 July 2009

[Original Full Text: LINK. EDITED.]


Executive summary

The interim ECDC risk assessment for Europe is that the 2009 pandemic influenza A(H1N1) virus will continue to spread, but many uncertainties remain. Though it seems that most of those infected in the US and in Europe experience a mild and self-limiting infection, this picture is still unclear as there has not been enough transmission to judge the effects, especially in those more at risk.

The indications from Europe and North America are that there are significant differences between the pandemic and the seasonal influenzas as regards more severe disease: there seems to be an underrepresentation of older people and a prominent representation of adults under the age of 60 with chronic ill health (including very obese persons), pregnant women, and very young children.

If confirmed this will have important implications for early treatment and vaccination policies.

Key features to note to date are:

• There are no reports as yet of unusual presentations or transmission routes for this influenza compared to normal seasonal influenza viruses. There is no indication of risk of infection through food or potable drinks.
• If the pandemic behaves like previous ones, cumulative clinical attack rates over the first major wave of infection in 2009?10 might be expected to be in the range of 20% to 30%, with a reasonable planning assumption of 30%.
• Based on experience in North America, clinical attack rates will be highest in children and younger adults.
• Adults over 60 years seem, at present, to be the least affected age group, though there are indications from the USA that those few that are affected experience the highest risk of severe disease of any age group.
• The groups experiencing most of the severe disease and death are those in the risk groups of people with chronic underlying medical conditions (this includes morbid obesity), pregnant women and young children (especially under two years of age).
• Most of those infected experience a mild self-limiting illness, even in people in risk groups. However, as for seasonal influenza there are some people who experience more severe disease and some of these die despite medical care. These include a few people without any known underlying condition and outside other risk groups.
• A reasonable planning estimate for hospitalisation rates in Europe using the overall clinical attack rate as a base is in the in the range 1% to 2%. However, in the winter this may rise because of the presence of other respiratory infections.
• Local experience from the USA (New York City) indicates that, without preparation, this pandemic can severely stress healthcare systems.
• The observed case fatality rate based on the largest population reported to date, from the USA, is 0.4%. While in Europe the observed rate in the earliest affected country (the United Kingdom) is 0.3%. However, this is likely to be higher than the true figure, which may at present be more than the range of 0.1% to 0.2% of all clinical cases.
• As in seasonal influenza, case fatality rates are high in the very young, low in children and young adults and then increase with age.
• At the individual level the highest risk of hospitalisation for an affected person is:
  
  • a) in the risk groups; and
  • b) for young children and those over 60.
• As yet almost all the viruses have been sensitive to the antivirals known as neuraminidase inhibitors (oseltamivir and zanamivir) but they are resistant to adamantenes (amantidine and rimantidine). There have been a few pandemic virus isolates that have showed resistance to oseltamivir (though sensitive to zanamivir).
• The current seasonal influenza vaccine that contains a component effective against another A(H1N1) virus is not effective against the new pandemic A(H1N1) 2009 virus.
• It is impossible to predict when European countries will be affected, but a proper first wave seems inevitable for the autumn. The experience in one country (the United Kingdom) suggests that countries could be affected considerably earlier in the autumn than happens with seasonal influenza.
• It is too early to predict what the mix of pandemic and seasonal influenza viruses will be this autumn, although there will also be B influenza viruses, as they do not compete with A viruses.
• Pandemic viruses are unpredictable, and can change their characteristics as they evolve. Even pandemics usually slow down in summer, only to pick up in autumn, and the virus may even then come back, perhaps in a more aggressive form, like it happened in 1918?19.
• ECDC will work with Member States, other European Agencies, the European Commission, WHO and its other international partners to gather more information to update this Risk Assessment at intervals. Special attention will be paid to how the pandemic is developing in the first affected European countries and the temperate Southern Hemisphere countries.

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