Dr. Andy

Reflections on medicine and biology among other things

Monday, May 16, 2005

More influenza

I’ve argued previously that the risk of an avian flu pandemic is overstated.

A Perspective piece (free full text!) in the May 5 NEJM says I’m wrong. Michael Osterholm argues that another influenza pandemic is a question of when, not if.
He raises some interesting points, including the increased risk of recombination between bird and human flu viruses with increasing affluence in China:
It is sobering to realize that in 1968, when the most recent influenza pandemic occurred, the virus emerged in a China that had a human population of 790 million, a pig population of 5.2 million, and a poultry population of 12.3 million; today, these populations number 1.3 billion, 508 million, and 13 billion, respectively. Similar changes have occurred in the human and animal populations of other Asian countries, creating an incredible mixing vessel for viruses. Given this reality, as well as the exponential growth in foreign travel during the past 50 years, we must accept that a pandemic is coming — although whether it will be caused by H5N1 or by another novel strain remains to be seen
I agree another pandemic will come eventually, but have said that advances in supportive care, along with anti-viral drugs should mitigate the scope of the problem, at least in rich countries

Osterholm says I’m wrong, that there just isn’t excess capacity in the system. For example, how many mechanical ventilators are there in the US?

About 105,000, of which 75-80K are in use at any given time. During a typical influenza season the number approaches 100K. So there isn’t much slack for an influenza pandemic. He thinks we will need temporary hospitals in high school gyms and community centers for up to 2 years to care for all the sick. Who will provide the care remains to be seen.

As far as deaths, he thinks it could be as bad as 1918
If we translate the rate of death associated with the 1918 influenza virus to that in the current population, there could be 1.7 million deaths in the United States and 180 million to 360 million deaths globally.
That would certainly be bad.

I’m still not convinced. SARS showed that isolation of the ill can control spread and I still think that supportive care and anti-virals would dramatically lower mortality rates. Previous influenza vaccines may provide some protection and a vaccine with at least partial efficacy could probably be produced quickly. It wouldn’t be perfect, but even an imperfect virus might slow the spread and give the immune system enough of a head start to dramatically decrease mortality.

I do agree we need to increase our commitment to research now, especially research towards developing an effective vaccine response.


At 7:54 AM, Anonymous Declan Butler said...

For a better appreciation of the limits of antiviral strategies, you should read

Containing Pandemic Influenza with Antiviral Agents
Ira M. Longini, Jr. , M. Elizabeth Halloran, Azhar Nizam and Yang Yang
Am J Epidemiol 2004; 159:623-633.

The US stockpile of drugs (2.3 million doses) is only enough to treat 1% of the population, and would go to first responders.

See also IOM workshop presentations on pandemic preparedness here

SARS and pandemic flu cannot be compared because of the much shorter incubation period of flu; it is also spread by asymptomatic patients. Model this and it is immediately obvious that the quarantine measures that worked for SARS will not work for pandemic flu -- at best they would delay spread.

Further reading on avian flu and pandemic risk can be found here

Declan Butler
Senior reporter, Nature
7 rue Guy de la Brosse
75005 Paris, France
Tel: (33) 1 43 36 59 90
d.butler@nature-france.com or d.butler@nature.com

My bookmarks: http://www.connotea.org/user/Declan

For science, read Nature… www.nature.com
…and for top science journalism: www.nature.com/news/


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