Risk Wise

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Preparing for the next influenza pandemic

Stephen C. Redd, US Centers for Disease Control and Prevention

severe influenza pandemic has the potential to be one of

the most catastrophic health events in history. This future

pandemic will happen when an influenza A virus circu-

lating in birds or other animals undergoes a genetic change that

allows it to be transmitted efficiently from person to person.

This genetic change can occur through a series of mutations or

through a process called reassortment, which occurs when a

person or animal is infected simultaneously with an animal

influenza virus and a virus that already has the capability to be

readily transmitted among people – some subsequent descen-

dent viruses could have genetic material from both viruses.

Should such a new virus emerge that can be readily transmitted

from person to person, the world would be on the verge of a

pandemic. Susceptibility to such a virus would be universal, the

illness it would produce could be severe, and without effective

control measures, transmission would be widespread. With

increasing global interconnectedness, an infection with the char-

acteristics of influenza – respiratory spread, initial non-specific

clinical manifestations, and a short incubation period – has the

potential to spread around the world in short order.

Unmitigated, a severe pandemic could cause tens of millions of

deaths worldwide, disrupt civil society, and lead to trillions of

dollars of economic losses over a period of months.

In late 2004 and through 2005 and 2006, the world

braced for an influenza pandemic caused by the H5N1

influenza virus. This virus had spread in poultry and wild

birds over the course of months through Asia and into

Europe and Africa, and although H5N1 was not readily

transmissible from person to person, there was wide-

spread concern regarding increasing chances that a series

of random mutations of the virus in an infected bird, or

genetic reassortment with an influenza virus better

adapted to human transmission, would ignite a pandemic.

In the face of these dire possibilities, modern science and

public health have expanded the repertoire of tools avail-

able to reduce the impact of an influenza pandemic since

the last influenza pandemic in 1968. These tools include

the capability to diagnose novel influenza virus infections

specifically and quickly, availability of anti-influenza drugs,

the technology to produce large quantities of vaccine well

matched against a pandemic influenza virus, and, although

not new, traditional public healthmeasures to reduce expo-

sure of susceptible persons to infectious persons. The global

challenge is to marshal these interventions into a rapid,

seamless, worldwide response for an inevitable event, but

one where the timing and severity are unpredictable.

The United States is working in partnership with other

national governments, numerous international organi-

zations, and internally, to prevent and prepare for the

next pandemic. In short, this work translates to plan-

ning and training to use the full range of interventions

available. Because the next pandemic will almost

certainly arise from an existing animal influenza virus,

monitoring such viruses and attempting to control or

eliminate them from animals is the first line of defence.

In the years since 2004, largely as a response to the

H5N1 threat, individual countries and the global

community have achieved a substantial level of

pandemic preparedness. Sustaining and improving

preparedness is now at risk because of complacency with

the H5N1 situation – the virus has not become more

transmissible from person to person – and because the

global economic climate favours dealing with current

problems rather than preparing for future ones.

Nevertheless, the current H5N1 threat is undiminished,

and the risk of a novel influenza virus, whether H5 or

another type, spawning a global pandemic is ever

present. Preparing for an influenza pandemic is an

ongoing effort, and the global community must be ever

vigilant to reduce the risk and prepare to mitigate the

consequences of the next influenza pandemic.

The H5N1 influenza virus spread rapidly in poultry and wild birds during 2004-2006

Image: US CDC