We are faced with the disturbing possibility of a new influenza pandemic. However, it is still unclear whether the new form of H1N1 influenza, first identified in Mexico, will spread easily around the world, and if so, how many deaths will result.
As in the 1918 pandemic, which killed up to 50 million people world-wide, this new virus has inherited some of its gene segments from swine influenza; other genes have come from bird influenza and from an earlier human influenza, through a process known as gene re-assortment, or shuffling.
This new virus is likely a single “lucky” survivor of such a gene reshuffle, probably occurring in a pig coincidentally infected with influenza viruses from different species. Such re-assortments, although rare, tend to occur in places where there are large numbers of humans and animals in potential contact, as in Asia and now, it seems, Mexico.
The good news is that the World Health Organization and most national governments have been preparing for such an emergency, spurred on most recently by the precedent of SARS and the continuing threat from H5N1 influenza in birds.
Antiviral agents such as oseltamivir and zanamivir have been stockpiled, and procedures have been developed to fast-track specific vaccines for any new pandemic strain. The current alert about this new H1N1 influenza has led public health authorities to enhance their surveillance to detect new cases, particularly amongst people who have travelled recently in affected countries.
Strategies for isolation and treatment of cases, and for protection or quarantine of at-risk groups are also well developed. Another piece of good news is that oseltamivir and zanamivir can be used to protect exposed health care workers from becoming ill (prophylaxis), and to reduce the severity of illness in at-risk persons if given early enough.
In the 1918-19 human pandemic, death rates were particularly high in isolated populations such as Alaska and Western Samoa, presumably because 90 years ago they were rarely visited by any (seasonal) influenza virus that could have left them with at least a degree of immune cross-protection against the 1918 H1N1 pandemic virus.
In contrast, many persons in urban populations reported no symptoms at all in any of the three waves of the 1918-19 pandemic. Detailed analysis suggests that even before the first pandemic wave, urban dwellers were protected by (temporary) prior immunity, contributing to their much lower rate of illness or death.
In our modern inter-connected world, virtually all persons are regularly exposed to seasonal influenza, so that average levels of cross-protective immunity could be even higher today than in 1918. It is also possible that influenza vaccine directed against seasonal influenza will confer additional short-lived protection against the new pandemic strain. If this is true, future studies of persons exposed to the new virus will show that illness is less severe amongst those with a history of prior vaccination.
Public health agencies around the world are cooperating hour-by-hour to monitor progress of this current threat and to improve the effectiveness of their control measures.
Although no-one can predict the outcome, we can be confident that our fate is in the best possible hands, and that with improved knowledge, and access to antivirals, antibiotics and vaccines, we are much better placed to deal with influenza and its complications than we were in 1918-19.
John D Mathews is a Professorial Fellow in the School of Population Health of the University of Melbourne, and Executive Director of the Menzies Foundation. These are his personal views.