The virus causes a mild flu pandemic , which mainly affects people born after H1N1 flu disappeared in However, the real surprise is that it does not displace the previous, and more virulent, seasonal flu, H3N2.
Instead, it continues circulating alongside it. The antibodies people produce after being infected by this new seasonal H1N1 do not protect against H1N1. However, infections also trigger another reaction called cell-mediated immunity, in which certain white blood cells target and destroy infected cells. Tests of the H1N1 pandemic vaccine show that, unlike antibodies, cell-mediated immunity to seasonal H1N1 may help protect against the pandemic virus. This does not prevent disease altogether, but can reduce its severity.
The predecessor of the H1N1 swine flu virus emerges in the US. It is a hybrid of human, bird and swine flu viruses , and by it is the dominant flu strain in US pigs. US pig farms try to control it with vaccines, but these attempts are largely ineffective because the virus evolves too rapidly, changing the surface proteins targeted by the vaccine while keeping its internal genes unchanged.
The pandemic virus is a variant on this flu, and behaves the same way. H5N1 flu, first identified as a threat to humans in Hong Kong in , spreads from Asia around the world, apparently carried by wild birds. H5N1 is also found in pigs in Indonesia , raising fears that it might reassort with other human flu viruses that pigs can harbour. These plans are made with the highly lethal H5N1 in mind, meaning that they are not always appropriate for the pandemic.
Pandemic fears boost spending on flu research. However, Indonesia, where most H5N1 outbreaks are happening, refuses to share samples of the virus , arguing that it will not benefit in return from any vaccines developed as a result.
But worries about H5N1 subside as it fails to become contagious in people — although virologists continue to warn that it is not the only threatening flu virus out there. Viruses from the H9 , H7 and H2 families all give cause for concern. The first cases of a new type of swine flu are reported in California and Texas in late March. Subsequent genetic analysis suggests that it may have started circulating in humans in January. On 27 April, with cases of suspected swine flu reported in Mexico, the World Health Organization WHO upgrades the pandemic warning level from 3 to 4 on a six-point scale.
Intensive efforts to understand the virus and develop a vaccine begin immediately. The US government advises against travel to Mexico , although research suggests that travel bans will not stop the virus spreading. Although swine flu seems to be spreading slowly , it is still progressing quickly enough to justify preparing for a pandemic.
However, the WHO delays declaring a pandemic , partly because there is not enough evidence that the virus is spreading in the general population outside the Americas, where it originated. New Scientist reveals that Europe is not testing people with flu symptoms unless they have recently travelled to an affected area in the Americas, or have had close contact with someone who did. As a result, Europe cannot detect spread in the general population. As concerns mount, it transpires that many countries are poorly prepared for this scenario and that supplies of H1N1 vaccine cannot be prepared in time to catch the second wave.
The UK and other countries change their rules and start testing people who have flu but no North American contacts. Cases of swine flu are soon detected.
As we write this, there are new rumors that the WHO is about to declare phase 4. We hope it does. Whether it does or not, we urge you to act as if it had. Don't get caught up in the phaseversus-phase-4 debate. What matters is that a pandemic looks likelier to materialize in the next few days, weeks, or months than it has looked for a long time. That's not a guarantee. The last time a pandemic looked pretty likely was the early days of the H5N1 spread through Asia—and the pandemic didn't happen.
The time before that was the first sighting of H5N1 in Hong Kong in —and it didn't happen then, either. The time before that, ironically, was the US swine flu scare of President Gerald Ford was alarmed enough about that one to launch a massive vaccination program to protect Americans from the pandemic—and that one didn't happen either. Flu experts are like hurricane forecasters. The weather map looks bad right now—but it's far from rare for hurricanes to fizzle out or change course.
Still, it would be exceedingly foolish not to take serious precautions when hurricane forecasters tell you a big one looks like it might be headed your way. The current economic crisis makes it difficult to argue for putting resources into pandemic planning when your company is just hanging on the ropes.
But that is exactly why you need to plan, because not having a plan all but ensures that your company will go under during a pandemic. If you've got a pandemic plan, you have thought this through already.
You have a list of things to do when a pandemic looks imminent but still iffy—actions that meet three key criteria that they:. You wrote the plan, hoping you'd never need to implement it—but figuring that sooner or later you might. Now you do implement it, but not the whole plan, at least not yet—just the easier bits. Well, for one thing, get your senior management to resolve right here and now that if the threat recedes this time, you'll do what it takes to have a plan in place—and tested—the next time a serious pandemic possibility looms.
In the meantime, put together a short list of things you can do now, even without a formal plan, to help your company brace for what may be just around the corner. Some things are probably too late to do—like stockpiling enough antivirals for your workforce and developing a protocol for getting them into their hands when they need it. But there's plenty you can do right now, this weekend, or early next week, that will help. Then if the pandemic threat fizzles or even if it stabilizes, hanging in abeyance for a few months , you can use the time to work on some longer-term preparedness measures.
Do these seven add up to a pandemic plan? And if you've got seven better ideas, implement yours instead. The main thing is this: A pandemic may be right around the corner, and you don't have a formal plan for how to cope. So be it. Now do what you can, as quickly as you can. And then if the pandemic hasn't come yet, do some more. His writing on risk communication can be found at www. Grant support for ASP provided by. Become an underwriter». All rights reserved.
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Apr 24, Share this page:. Here's what we know today: 1. It's settled. Swine flu is killing people in Mexico. Whether you call it phase 3 or phase 4, now is the time to implement the preliminary parts of your pandemic plan. In the case of swine flu, we may have acted too soon. And in the case of AIDS, we may have acted too slowly. Read the book by Neustadt and Fineberg 3 for a full account of our perceived folly in regard to swine flu.
I relate these personal reminiscences because many who read this article will be on the firing line when future epidemics threaten, and they may either erupt or fizzle out. You will be in a fog, and you will need to exercise the best judgment you can on the basis of available surveillance information and historical context. Roy Anderson and others have been on the firing line in the United Kingdom with bovine spongiform encephalopathy and foot-and-mouth disease.
And now any number of national and international organizations and the ministries of health in many countries in Southeast Asia are on the firing line in regard to avian influenza. Should we stockpile drugs? Prepare a vaccine? Cull infected flocks? When difficult choices arise, criticism is almost certain to follow, but as Harry Truman said, "If you can't stand the heat, stay out of the kitchen. Any narrative on the swine flu episode would be incomplete without mentioning the work of Richard Shope on the possible relationship between the putative influenza virus of and its eventful residence in pigs in Iowa, where it caused an influenzalike syndrome and where it remained as a reservoir 5.
Whatever the merits of this argument about the cause of swine flu virus infection in adults in the s, of interest here is Francis's suggestion that the swine flu antibody in humans was the result of repeated exposure to human strains, and perhaps not due to prior infection with the virus.
Surely his thoughts about this matter were the genesis of the concepts expressed in On the Doctrine of Original Antigenic Sin, published in 6.
Francis wrote, "The antibody of childhood is largely a response to dominant antigen of the virus causing the first type A influenza infection of the lifetime. The antibody-forming mechanisms are highly conditioned by the first stimulus, so that later infections with strains of the same type successfully enhance the original antibody to maintain it at the highest level at all times in that age group.
The imprint established by the original virus infection governs the antibody response thereafter. This we have called the Doctrine of the Original Antigenic Sin. Francis died in and did not live to know the full explanations for antigenic shift through reassortment of gene segments from 2 parent viruses or antigenic drift through mutation.
He surely would have been in awe, as we all are, of the molecular explanation of influenza virus variation with succeeding epidemics. And yet, even with the brilliant work of Taubenberger delineating the virus 7 , we can still ask Francis's question: Which strain will cause the next pandemic? Francis would have been cautious, but he certainly would have agreed that knowing the genetics of the virus will guide our strategy to confront future influenza pandemics. And I believe he would be cautious about the pandemic potential of the current avian influenza virus.
He would warn us to keep alert to the unexpected, to be prepared for a "newe acquayantance. The persistent theme underlying his research concerns the substances in bacteria that stimulate the body's immune system and the genetic factors that influence the immune response.
Specifically, he has been involved in wide-ranging studies on the microbiology and immunology of streptococcal infections. Suggested citation for this article : Krause R. The swine flu episode and the fog of epidemics. Emerg Infect Dis [serial on the Internet]. Krause, Introduction, pages 1—22, Copyright , with permission from Elsevier.
National Center for Biotechnology Information , U. Journal List Emerg Infect Dis v. Emerg Infect Dis. Author information Copyright and License information Disclaimer. Corresponding author. Copyright notice. This article has been cited by other articles in PMC. Abstract The influenza pandemic has shaped research and public health for nearly a century. Keywords: influenza, swine flu, pandemics.
Early Experiences with Influenza At the beginning of the 20th century, the fact that many contagious diseases were caused by microbes was well established, but at the time no treatment was available for any of them except syphilis and malaria.
The Fog of Epidemics The uncertainty that surrounds any response to a microbial outbreak, the "fog of epidemics," is analogous to the fog of war, of which historians speak 2. Original Antigenic Sin Any narrative on the swine flu episode would be incomplete without mentioning the work of Richard Shope on the possible relationship between the putative influenza virus of and its eventful residence in pigs in Iowa, where it caused an influenzalike syndrome and where it remained as a reservoir 5.
Acknowledgment I thank Lulu Marshall for her assistance with the preparation of this manuscript.
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