The threat of a second infection wave needs to be taken seriously
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.
We asked McCaw: 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, 1957 and 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 H1N1 virus, 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
Thus, 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 and 1968.
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 in 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 (i.e., 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 healthy 20- to 40-year-old individuals, whose immune system reacts more vigorously to the infection.
H1N1 and H5N1 may co-mingle
Mutations are not the only concern. Scientists are worried about the possibility that the swine flu virus might co-mingle with the highly deadly bird flu A(H5N1) virus.
Looking at the Southern Hemisphere
Important clues about the likelihood of a lethal
swine flu pandemic in the fall may come from the Southern Hemisphere, where the influenza season is just about to begin. Scientists and healthcare officials are actively monitoring the virus’ behavior in those countries, with particular attention to Colombia, Costa Rica, Guatemala and El Salvador. This would enable them to determine whether the swine flu outbreak is actually becoming more severe. The hope is to use such information to develop more effective pandemic plans.
Pandemic Preparedness may help reduce mortality
One thing’s for sure: “Putting in place systems that will quickly detect any sign of increasing severity or an upsurge in cases following the first wave is a priority,” says McCaw. “
Pandemic planning, including antiviral distribution strategies and vaccination preparation efforts, need to work on the assumption that a second wave may occur. And that it may be more severe than the first.”
Of particular relevance, in this regard, are the findings of a 2006 re-analysis of the Spanish pandemic influenza of 1918, led by professor John Oxford, of the Centre for Infectious Diseases, Bart’s and the London, Queen Mary’s School of Medicine and Dentistry, London, UK.
Oxford’s team found that, contrary to common belief, most of the people infected with the
swine flu A(H1N1) virus during the 1918 Spanish flu survived. This, despite the fact that vaccines and antiviral medications were not available at that time. If this tells us anything, it’s that “judicious and careful planning… could help reduce mortality in a new pandemic to figure significantly less than 1918,” says Oxford.
“There is every reason as we face the first pandemic of the 21st century that we can be optimistic,… turn again to history… and return to Churchill for inspiration ‘give us the tools and we will finish the job.’”
Major differences between then and now
A vaccine to protect us in the event of a deadlier swine flu outbreak in the fall is being prepared in countries across the globe. As mentioned above, together with the availability of antiviral medications, this is one major difference between now and the Spanish flu pandemic of 1918-19. However, there is no guarantee that the vaccine will be ready in time, or even effective, because the virus may change in the meantime. And, almost certainly, there will not be enough of it for everyone.
There is also the likelihood that, by fall, the swine flu A(H1N1) virus might become resistant to antiviral medications, hampering any effort of treatment when most needed, as millions of people will likely be infected.
Probably not better off than in 1918
What is the most likely scenario for the world in the eventuality of a second, more severe, wave of swine flu? Experts say this may be more similar than expected to what was experienced during the 1918 Spanish flu pandemic. Of particular concern is hospitals’ supposedly inability to cope with increasingly large numbers of patients, at a time in which a severe shortage of healthcare professionals, due to sickness, and lack of adequate medical supplies and medications are highly likely. Fear may play a role, as well.
“[During the Spanish flu], fear of contagious kept caregivers from performing their duties,” says Dr. Monica Schoch-Spana, of the Center for Civilian Biodefense Strategies at the Johns Hopkins University, in Baltimore. “Hospitals were crippled by influenza’s hold on urban population… shortage of… linens, mattresses, bedpans, and gowns arose in some instances.”
“Despite 80 years of medical advances and expansive growth in the health care industry, there remains great uncertainty about our capacity to respond to an infectious disease emergency,” says Schoch-Spana. “In many respects, we may be at a disadvantage today compared with 1918. Then, most people were cared for by family members. Patients did not rely heavily on paid health professionals, nor did they expect today’s sophisticated standards of care.”
Intentional exposure to the A(H1N1) virus should be avoided
Lastly, health officials warn that getting swine flu, now, does not necessarily give immunity to further more severe infections. One reason for this is that the virus may not be the same in a few months, as a result of mutations.
Another, and most important, reason is that too little is known about how the swine flu A(H1N1)virus reacts in any one individual. It may cause severe disease and death. Consequently, intentionally mixing with people who have swine flu in the hope of being infected should be avoided.
FLU PANDEMIC DÉJÀ VU. In 1918, the A(H1N1) outbreak began in the spring, with a relatively small and localised death rate, from a mild strain of the flu virus, which spread rapidly. Known as Spanish flu, its infection and mortality rate slowed during the summer, but come fall, as temperatures cooled, a much more lethal strain of the virus evolved, killing millions, around the globe. All the signs now suggest the same will happen again soon, this year. In the US alone, the WHO is predicting a possible 7 percent swine flu infection rate. And that could be a conservative estimate. Dr. Howard Markel, of the University of Michigan, an eminent expert on pandemics, says: “...There may be a case fatality rate of 1 or 2 percent and it doesn’t sound like very much, but seasonal flu kills about 35,000 a year (in the United States) and has a case fatality rate of .01 to .02 percent.”
References
Mathews J.D., McCaw C.T., Mcvernon J., McBryde E.S., Mccaw J. “A biological model for influenza transmission: pandemic planning implications of asymptomatic infection and immunity,” PLoS ONE, 2007, 2(11): e1220. doi:10.1371/journal.pone.0001220
Munster V.J., de Wit E., van den Brand J.M.A, Herfst S., Schrauwen E.J.A., Bestebroer T.M., van de Vijver D., Boucher C.A., Koopmans M., Rimmelzwaan G.F., Kuiken T., Osterhaus A.D.M.E., Fouchier R.A.M. “Pathogenesis and transmission of swine–origin 2009 A(H1N1) influenza virus in ferrets,” Science, July 2, 2009, 10.1126/science.1177127.
Oxford J.S., Lambkin R., Elliot A., Daniels R., Sefton A., Gill D. “Scientific lessons from the first influenza pandemic of the 20th century,” Vaccine 2006, 24:6742-6746.
Schoch-Spana M. “’Hospital’s full-up’” The 1918 influenza pandemic,” Public Health Reports, 2001, 116(suppl.2):32-3.
Labels: A(H1N1), epidemic, flu, H5N1, influenza, outbreak, pandemic, preparedness, spanish, swine, vaccination, virus
