The current swine flu pandemic has, so far, turned out to be less severe than expected, with most infected people experiencing mild symptoms, and only a relatively limited number of deaths.
Will it stay this way and slowly fade away?
Health officials say this is unlikely, and warn that swine flu may re-emerge,next fall, more deadly than ever. There remains, however, uncertainty about what could happen should this relatively mild outbreak be followed by a more severe one later this year.
Dr. James McCaw, of the Vaccine & Immunization Research Group (VIRGo), in the School of Population Health at the University of Melbourne, Australia, is involved in major math modeling projects related to pandemic influenza transmission, immunity and threat.
McCaw was asked what is the likelihood of a second wave of swine flu? And what should we expect over the coming months?
Flu pandemics historically come in waves We know from past pandemics that multiple waves can, and do, occur, says McCaw. A defining feature of pandemics, like the ones of 1918-19, 1957and 1968, is their tendency to occur out-of-season, not necessarily over the winter period.
The 1918-19 pandemic (i.e., the Spanish flu), which was also caused by the H1N1virus, provides the best example of this type of behavior, he says. At that time, the United States and the United Kingdom experienced three distinct H1N1 flu waves, within just 12 months.
McCaw notes that each wave was more severe than seasonal influenza, both in terms of the proportion of the population infected and the case fatality rate. The second wave in the United Kingdom was the most severe, contributing the most deaths of any of the three waves. And the severity of influenza remained high for a number of seasons following the pandemic.
Beyond a second wave It appears that the wave behavior might extend beyond a second flu outbreak into possible further flu pandemic waves. There is clear evidence that this happened in the past, says McCaw, as shown by an increase in the numbers and severity of the seasonal flu outbreaks that occurred after a pandemic. This was the case, for example,for many populations around the world after the Spanish flu and the flu pandemics of 1957 and1968.
Predictions are difficult to make In terms of the 2009 outbreak, he says, we have very little data that would allow prediction of a second wave, let alone its severity. As such, we cannot specify a probability or the 'likely characteristics'of a second wave.
New research confirms: swine flu could turn deadlier For a lethal fall swine flu pandemic wave to occur, the A(H1N1) virus needs to mutate into a form capable of infecting and killing more people, more rapidly. Although, there is no firm evidence that the swine flu virus is already undergoing such a transformation,a study published is Science by researchers of the National Influenza Center and Department of Virology, Erasmus Medical Center, Rotterdam, the Netherlands,shows that it has indeed the potential of becoming more deadly.
Compared to previous seasonal influenza A(H1N1) forms, which only replicate in the upper airways (i.e., the nasal cavity), 2009 A(H1N1) has the ability, in animals,of reproducing in the lower airways ( trachea, bronchi, and lungs). What this means to us is that 2009 A(H1N1) could trigger a highly deadly form of viral pneumonia capable of killing people in just a few hours, as it occurred during the Spanish flu of 1918. Most at risk would be healthy20- to 40-year-old individuals, whose immune system reacts more vigorously to the infection.
Don't just write Swine Flu off as another minor problem as the second wave could kill us all.
Mark, a good article but your timing might be a little off. You say it will re-emerge NEXT fall- when in reality it is already emerging and will increase in cases within the next four weeks. Thanks for the article JP
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