isirv

By Douglas Fleming, OBE, FMedSci

In the last five years, influenza experts have been particularly concerned with the potential of an avian flu virus (sub-type A [H5N1]) as a likely cause of a pandemic. We have now to contend with the pandemic threat of an A (H1N1) virus of swine origin. There have been many winter influenza epidemics attributable to H1N1 viruses but the virus recently identified as the cause of the epidemic in Mexico is substantially different from any previous H1N1 virus infecting humans. Society generally has very little innate or acquired immunity to it. Unlike the H5N1 avian virus where transmission between humans is quite exceptional, there is clear evidence that this virus spreads readily from person to person thus giving rise to the pandemic threat.

The fear engendered by the word pandemic relates to the historic epidemic of 1918 and its impact on morbidity and mortality. Since then, there have been at least two worldwide pandemics and a limited outbreak of swine flu in the United States of America in 1976; all of which have been much less severe in their impact than was seen in 1918. Though the present outbreak does not appear to have caused widespread severe illness, we need to recognize that pandemic conditions have often been preceded by periods of less severe disease and limited spread; conditions which have been described as a “herald wave.”

Appropriate response to these herald wave conditions includes heightened surveillance and the development and manufacture of a strain-matched vaccine. Development of a strain-matched vaccine will be challenging in light of the need for continued production of seasonal vaccines. Heightened surveillance means more rigorous investigation of persons with acute respiratory infections whether they meet classical case definition criteria or not. Whilst early indications suggest that this virus is not causing severe illness, we must not assume that this will remain so. As part of the scientific community particularly concerned with influenza, we call on all physicians to be diligent in their investigation of acute respiratory infections. A mild disease, which may be responsible for minor illness at the moment, must not allow us to become complacent. Furthermore, the threat of an H5N1 pandemic continues and is not diminished by the emergence of this H1N1 swine virus. Continuing high quality surveillance is essential.

Dr Douglas Fleming, OBE, FMedSci, is the Director of the Royal College of General Practitioners Research and Surveillance Centre, Birmingham, England.