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<recommendedContent xmlns="http://api.mspoke.com">
    <recommendedItem id="20100101_19_414"
                     title="H1N1 Vaccination Still a Good Idea, CDC Says"
                     score="0.014"
                     href="http://www.medpagetoday.com/InfectiousDisease/SwineFlu/tb/18325?impressionId=1265755341598"
                     
      &lt;p&gt;Although pandemic H1N1 influenza activity appears to have leveled off, the CDC remains wary of what the future may hold.&lt;/p&gt;
&lt;p&gt;No states were reporting widespread influenza activity, and only six  --  Alabama, Georgia, Maine, New Jersey, New Mexico, and Virginia  --  were reporting regional activity, Anne Schuchat, MD, director of the CDC&apos;s National Center for Immunization and Respiratory Diseases, told reporters on a conference call today.&lt;/p&gt;
&lt;p&gt;Influenza-like activity remained below the baseline level for this time of year for the third straight week, Schuchat said.&lt;/p&gt;
&lt;p&gt;&quot;That&apos;s fairly similar to what we would normally see at this time of year with seasonal flu,&quot; she said.&lt;/p&gt;
&lt;p&gt;However, she said that the H1N1 virus continues to circulate, causing severe disease and death in some cases.&lt;/p&gt;
&lt;p&gt;Although total activity is down, Schuchat noted that the proportion of deaths attributed to either flu or pneumonia is higher than the epidemic threshold, and has been for the past three weeks. The reasons were unclear, but she said there are no indications that the virus has become more virulent.&lt;/p&gt;
&lt;p&gt;But, she said, &quot;H1N1 vaccination remains a good idea.&quot;&lt;/p&gt;
&lt;p&gt;The most recent results of the CDC&apos;s National H1N1 Flu Survey revealed that about 70 million people, or 23.4% of Americans, have been vaccinated so far. About 76 million doses of the vaccine have been used because of the requirement that children younger than 10 get two.&lt;/p&gt;
&lt;p&gt;About 37% of children up to age 18 have been vaccinated. For those younger than 10, 37% have received their second dose.&lt;/p&gt;
&lt;p&gt;Vaccine supply remains ample, Schuchat said, with about 124 million doses shipped around the country up to this point.&lt;/p&gt;
&lt;p&gt;Citing an &quot;unprecedented&quot; effort to monitor safety, she said there have not been any major safety concerns identified.&lt;/p&gt;
&lt;p&gt;&quot;So if safety was the reason that you were waiting, I think you can be reassured on that front.&quot;&lt;/p&gt;

    </recommendedItem>
    <recommendedItem id="20100101_19_302"
                     title="WHO Calls H1N1 Response Imperfect"
                     score="0.006"
                     href="http://www.medpagetoday.com/InfectiousDisease/SwineFlu/tb/18165?impressionId=1265755341598"
                     
      &lt;p&gt;The World Health Organization says its response to the H1N1 pandemic could have been better, but was not unduly swayed by drug manufacturers.&lt;/p&gt;
&lt;p&gt;&quot;We are under no illusions that this response was the perfect response,&quot; Keiji Fukuda, MD, the agency&apos;s top flu expert, told a hearing being held by the Council of Europe&apos;s health committee.&lt;/p&gt;
&lt;p&gt;But he added, &quot;The influenza pandemic policies and responses recommended and taken by WHO were not improperly influenced by the pharmaceutical industry.&quot;&lt;/p&gt;
&lt;p&gt;The council&apos;s hearing is a response to criticism by some European politicians, as well as elements of the media, that the danger of the H1N1 pandemic was exaggerated, perhaps to allow drug companies to score multimillion-dollar contracts for vaccines and antivirals.&lt;/p&gt;
&lt;p&gt;In North America, many experts defended the response to the outbreak, which WHO last April declared a phase six pandemic  --  the highest level. The phases reflect that an infectious agent is widely spread and causing disease in the community, but they say nothing about the severity of the disease.&lt;/p&gt;
&lt;p&gt;&quot;I do not believe that the record supports the claim that health officials in the U.S. or WHO exaggerated the threat,&quot; said Andy Pavia, MD, of the University of Utah in Salt Lake City.&lt;/p&gt;
&lt;p&gt;Pavia said in an e-mail that health officials had a choice  --  to assume the threat was minor or to react strongly.&lt;/p&gt;
&lt;p&gt;&quot;The choice is obvious,&quot; Pavia said, &quot;and I would not want to be in a position of explaining to the families of victims why we planned for the mildest outcome.&quot;&lt;/p&gt;
&lt;p&gt;For the most part, illness caused by the disease has been mild, although several thousand people have died around the world and many more were sick enough to require intensive care.&lt;/p&gt;
&lt;p&gt;But the relatively low number of deaths has prompted Wolfgang Wodarg, MD, a German member of the council&apos;s Parliamentary Assembly, to dub the outbreak a &quot;false pandemic&quot; and call for this week&apos;s hearing.&lt;/p&gt;
&lt;p&gt;&quot;What we have experienced now is that millions of people have been vaccinated unnecessarily,&quot; Wodarg said. &quot;This is damage done to people, in order to earn money.&quot;&lt;/p&gt;
&lt;p&gt;Fukuda, on the other hand, said today the pandemic &quot;is a scientifically well-documented event.&quot;&lt;/p&gt;
&lt;p&gt;&quot;The labeling of the pandemic as &quot;fake&quot; is to ignore recent history and science,&quot; he said, &quot;and to trivialize the deaths of over 14,000 people and the many additional serious illnesses experienced by others.&quot;&lt;/p&gt;
&lt;p&gt;Utah&apos;s Pavia echoed that sentiment. Ask any front-line doctor if the H1N1 flu was mild, he said, &quot;and prepare to get your head handed to you.&quot;&lt;/p&gt;
&lt;p&gt;One of them was Daniel Hinthorn, MD, of the University of Kansas Medical Center in Kansas City, Kan. &quot;As a physician who saw many patients with this disease, I believe it was very serious in many people,&quot; he wrote in an e-mail. &quot;The threat was not exaggerated, at least to my mind.&quot;&lt;/p&gt;
&lt;p&gt;Even last month, as flu activity in the U.S. declined, he said his hospital treated 11 inpatients for the flu, including six in intensive care, while &quot;lots of others&quot; were being seen in emergency wards and clinics.&lt;/p&gt;
&lt;p&gt;On the other hand, to say the threat was exaggerated &quot;is merely to say the obvious,&quot; argued Philip Alcabes, PhD, of City University of New York City. By the time a vaccine was available, &quot;this outbreak was far less serious than feared,&quot; he said in an e-mail.&lt;/p&gt;
&lt;p&gt;But &quot;reality-based skepticism about swine flu&quot; doesn&apos;t mean that people would refuse immunization  --  not if an outbreak was a real public danger, caused by a &quot;highly transmissible agent, likely to be virulent, highly preventable with reliably effective vaccine.&quot;&lt;/p&gt;
&lt;p&gt;He warned that public health professionals must avoid &quot;falling in love with the most dire forecast and then pushing high-tech precautions against the worst-case scenario.&quot;&lt;/p&gt;
&lt;p&gt;When that happens, &quot;people have to be excused for wondering whether the officials, the media, and the pharmaceutical companies were in cahoots on swine flu,&quot; he said.&lt;/p&gt;
&lt;p&gt;But several experts argued that preparing for a worst-case scenario was the responsible thing to do.&lt;/p&gt;
&lt;p&gt;Sometimes, &quot;mother nature throws us a break,&quot; argued Howard Markel, MD, PhD, of the University of Michigan in Ann Arbor.&lt;/p&gt;
&lt;p&gt;&quot;We responded to a threat without knowing the future,&quot; he said in an e-mail. &quot;A far worse outcome might have occurred if we did not take the threat seriously and H1N1 turned out to be worse than we initially predicted.&quot;&lt;/p&gt;
&lt;p&gt;The public health response should be compared to the use of seat belts or auto insurance, according to Gregory Poland, MD, of the Mayo Clinic in Rochester, Minn.&lt;/p&gt;
&lt;p&gt;Every day, he said in an e-mail, he puts on his seat belt before driving. &quot;I don&apos;t finish each day and say &apos;What a waste, I didn&apos;t have an accident,&apos;&quot; he said.&lt;/p&gt;
&lt;p&gt;&quot;It is (and remains) unpredictable as to whether this virus could further mutate or change in a manner such that it could literally turn deadly within weeks,&quot; he said. &quot;If this pandemic had been deadly (and you don&apos;t know until you are into it) and we weren&apos;t prepared, the criticism would have been overwhelming.&quot; Poland said.&lt;/p&gt;
&lt;p&gt;He and others also noted that the flu season isn&apos;t over yet.&lt;/p&gt;
&lt;p&gt;&quot;This argument should be taking place at the end of the flu season in late March, not now,&quot; said Peter Katona, MD, of the University of California Los Angeles. &quot;Flu is unpredictable, and this is the heart of the argument.&quot;&lt;/p&gt;
&lt;p&gt;&lt;em&gt;This article was developed in collaboration with ABC News. &lt;/em&gt;&lt;img src=&quot;http://www.medpagetoday.com/upload/2009/10/1/14357_1.jpg&quot; mce_src=&quot;http://www.medpagetoday.com/upload/2009/10/1/14357_1.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;
    </recommendedItem>
    <recommendedItem id="20100101_19_160"
                     title="CDC Says 20% of Americans Got H1N1 Flu Shot"
                     score="-0.004"
                     href="http://www.medpagetoday.com/InfectiousDisease/SwineFlu/tb/17990?impressionId=1265755341598"
                     
      &lt;p&gt;As 2009 ended, an estimated 55 million Americans had been infected with the H1N1 pandemic flu and roughly one in five Americans had been vaccinated against the disease, the CDC said.&lt;/p&gt;
&lt;p&gt;The immunization data works out to about 61 million people, the agency said in an early release issue of &lt;em&gt;Morbidity and Mortality Weekly Report&lt;/em&gt;.&lt;/p&gt;
&lt;p&gt;The proportion of people vaccinated was higher among those in priority groups, the agency said, including 29.4% of children ages 6 months through 18 years and 38% of pregnant women.&lt;/p&gt;
&lt;p&gt;At the same time, the CDC issued new estimates of the toll taken by the pandemic virus since the outbreak began last April: &lt;ul&gt; &lt;li&gt;About 55 million people had been infected up to Dec. 12, although the estimates ranged from 39 million to as high as 80 million.&lt;/li&gt; &lt;li&gt;About 246,000 needed inpatient care, although the number ranged from 173,000 to 362,000. &lt;/li&gt; &lt;li&gt;And about 11,160 died, with the estimate ranging from 7,880 to 16,460.&lt;/li&gt; &lt;/ul&gt;&lt;/p&gt;
&lt;p&gt;The vaccination findings are based on two surveys  --  the National 2009 H1N1 Flu Survey and the Behavioral Risk Factor Surveillance System survey, which took place from Dec. 27 to Jan. 2 and from Dec. 1 to 27, respectively.&lt;/p&gt;
&lt;p&gt;Because vaccine was expected to be in short supply at the beginning, the CDC established initial target groups, including pregnant women, people living with or caring for infants under 6 months, healthcare and emergency medical services personnel, children and young adults, and adults with certain medical conditions.&lt;/p&gt;
&lt;p&gt;The CDC estimated that 27.9% of those people got vaccinated.&lt;/p&gt;
&lt;p&gt;The agency said the vaccine supply is now &quot;ample&quot; and efforts to promote general vaccination should continue.&lt;/p&gt;

    </recommendedItem>
    <recommendedItem id="20090101_19_1294"
                     title="IVW: Pandemic Vaccines May be Too Little, Too Late"
                     score="-0.005"
                     href="http://www.medpagetoday.com/InfectiousDisease/SwineFlu/tb/13943?impressionId=1265755341598"
                     
      CANNES, France, April 28 -- If the swine flu outbreak develops into a pandemic -- and that&apos;s a big if -- the earliest the public would see a vaccine against the disease would be September, a researcher said here at the conference on Influenza Vaccines for the World.
              &lt;br&gt; 
              &lt;br&gt;And that&apos;s if the government asks industry to start production today, said Klaus Stohr, D.V.M., vice president and global head of Novartis Vaccines and Diagnostics and former head of the World Health Organization&apos;s global influenza program.
              &lt;br&gt; 
              &lt;br&gt;&quot;What we have seen the last two or three days is that the current pandemic vaccine system is not ideal not only in terms of timing . . . but also in terms of vaccine production,&quot; he said.
              &lt;br&gt; 
              &lt;br&gt;Any hopes that the version of H1N1 in the current seasonal vaccine would provide protection against the swine flu seemed to be dashed by preliminary data from Novartis-run tests.
              &lt;p&gt; 
              &lt;p&gt;Dr. Stohr said the findings suggested the H1N1 viruses contained in seasonal vaccines all the way back to 1980 are more closely related to each other than any are to the new virus, although he cautioned that more study was needed before concluding that there wouldn&apos;t be cross-protection.
              &lt;p&gt; 
              &lt;p&gt;He said that the outbreak of swine influenza A H1N1 has not changed &quot;the assessment that pandemic vaccines are too little, too late, and that they are not going to be a solution even for countries that have domestic vaccine production.&quot;
              &lt;p&gt; 
              &lt;p&gt;Based on the current state of the swine flu investigation -- ongoing clinical, epidemiological, and virological studies -- it would take about two weeks for vaccine strain preparation, he said.
              &lt;p&gt; 
              &lt;p&gt;Seed virus preparation would take another three or four weeks, putting the start of bulk production at the end of June, Dr. Stohr said.
              &lt;p&gt; 
              &lt;p&gt;Standardizing reagents would not be available for another eight weeks, and quality control would tack on an additional one to two, he said.
              &lt;p&gt; 
              &lt;p&gt;Only then, in early September, would Novartis and other vaccine makers start distributing vaccine, he said.
              &lt;p&gt; 
              &lt;p&gt; 
              &lt;p&gt;Any decisions regarding pandemic vaccine production, he said, are complicated by the fact that nobody knows whether the virus will cause a pandemic, become endemic in humans causing continuous small outbreaks, or fizzle out and disappear.
              &lt;p&gt; 
              &lt;p&gt;If the virus were to &quot;disappear&quot; though, that would not necessarily eliminate the need to prepare for its re-emergence if it remained in an animal reservoir, Dr. Stohr said.
              &lt;p&gt; 
              &lt;p&gt;A possible solution would be development of a tetravalent seasonal flu vaccine, he said.
              &lt;p&gt; 
              &lt;p&gt;Further complicating decision-making is the looming threat of an H5N1 avian flu pandemic.
              &lt;p&gt; 
              &lt;p&gt;&quot;The absolute risk of H5N1 to cause a pandemic has not changed,&quot; he said. &quot;It remains a strain with high pandemic potential.&quot;
              &lt;p&gt; 
              &lt;p&gt;Swine flu, however, has bumped it down to number two on the list, he said.
              &lt;p&gt; 
              &lt;p&gt;The swine flu outbreak serves as &quot;a stark reminder of the unpredictability of the timing and of the speed by which the pandemic situation can change,&quot; he said.
&lt;p&gt;
&lt;p&gt;&lt;a href=&quot;http://www.medpagetoday.com/InfectiousDisease/SwineFlu/&quot; title=&quot;Swine Flu Coverage&quot;&gt;&lt;img src=&quot;/images/swine.jpg&quot; border=&quot;0&quot;&gt;&lt;/a&gt;

    </recommendedItem>
    <recommendedItem id="20090101_19_1337"
                     title="Tsunami of Swine Flu News Leaves World Awash in Questions"
                     score="-0.005"
                     href="http://www.medpagetoday.com/InfectiousDisease/URItheFlu/tb/14005?impressionId=1265755341598"
                     
      TORONTO, April 30 - After a bewildering week of breakneck developments, there are still huge gaps in our understanding of the 2009 H1N1 (swine flu) outbreak.
              &lt;p&gt; 
              &lt;p&gt;But experts agree that this mysterious flu strain provides both a threat and an opportunity.
              &lt;p&gt; 
              &lt;p&gt;The flu is a threat because it&apos;s a new virus, or &quot;reassortant.&quot; Few if any people have a preexisting immunity to it, according to Joan Nichols, Ph.D., of the Galveston National Laboratory in Texas.
              &lt;p&gt;         &lt;div class=&quot;APL&quot;&gt;

&lt;span class=&quot;bbr_hd&quot; style=&quot;font-size:11px;&quot;&gt;In this story: &lt;hr width=&quot;80%&quot; style=&quot;border:thin dotted #9b9b9b; border-style: none none dotted;&quot;/&gt;&lt;ul&gt;&lt;li class=&quot;APP&quot;&gt;&lt;a href=&quot;#heat&quot;&gt;Plenty of heat but little light so far&lt;/a&gt;&lt;/li&gt;&lt;br&gt;&lt;li class=&quot;APP&quot;&gt;&lt;a href=&quot;#mild&quot;&gt;Most Mexican Cases Could Be Mild&lt;/a&gt;&lt;/li&gt;&lt;br&gt;&lt;li class=&quot;APP&quot;&gt;&lt;a href=&quot;#evolution&quot;&gt;An unprecedented look at viral evolution&lt;/a&gt;&lt;/li&gt;&lt;br&gt;&lt;li class=&quot;APP&quot;&gt;&lt;a href=&quot;#worrisome&quot;&gt;Lack of immunity makes this virus worrisome&lt;/a&gt;&lt;/li&gt;&lt;br&gt;&lt;li class=&quot;APP&quot;&gt;&lt;a href=&quot;#severity&quot;&gt;A new scale for pandemic severity&lt;/a&gt;&lt;/li&gt;&lt;/ul&gt;&lt;/span&gt;&lt;/div&gt;
              &lt;p&gt;&quot;Everyone has the potential to be infected by this,&quot; she said, although whether that will lead to a serious public health menace remains unclear. 
              &lt;p&gt; 
              &lt;p&gt;On the other hand, the World Health Organization -- acting with dispatch on fragmentary information -- raised the pandemic threat level twice this week.
              &lt;p&gt; 
              &lt;p&gt;That was an early signal to countries around the world to get their public health machines in gear. It was also the first real test of world public health efforts since the 2003 outbreak of Sudden Acute Respiratory Syndrome (SARS).
              &lt;p&gt; 
              &lt;p&gt;Don Low, M.D., of Toronto&apos;s Mount Sinai Hospital, who was at the heart of the SARS fight in a key battleground, said the public health response is &quot;absolutely&quot; better this time around.
              &lt;p&gt; 
              &lt;p&gt;Among other things, he said, the scientific establishment is better equipped to deal with novel viruses and -- perhaps vitally -- the alarm bells rang quickly this time. 
              &lt;p&gt; 
              &lt;p&gt;SARS, he pointed out, was circulating - and causing serious sickness - in the fall of 2002. Yet it was only in the spring of 2003 that clinicians in Toronto realized they had a novel disease on their hands.
              &lt;p&gt; 
              &lt;p&gt;In contrast, the 2009 &quot;swine flu&quot; was identified with startling speed. The CDC notified WHO on April 17 that an unknown H1N1 influenza virus had been isolated from a person in California. 
              &lt;p&gt; 
              &lt;p&gt;The same day, Mexico was asking Canada&apos;s national microbiology lab for help in identifying the cause of an outbreak of respiratory illness there. Four days later, researchers knew that the Mexican disease was caused by the strange virus CDC had turned up.
              &lt;p&gt; 
              &lt;p&gt;The next day, April 23, CDC announced that the threat existed. Since then, the news feed has not stopped. Both CDC and WHO have held news briefings at least once a day, sometimes twice.
              &lt;p&gt; 
              &lt;p&gt;&quot;There has been great communication with the public,&quot; Dr. Low said.
              &lt;p&gt; 
              &lt;p&gt;Dr. Nichols called the speed of the reaction amazing. &quot;We really quickly caught it,&quot; he said.
              &lt;p&gt; 
              &lt;p&gt;Indeed, extensive pandemic planning is paying off, according to Richard E. Besser, M.D., CDC&apos;s acting director. &quot;The fact that we have been exercising several times a year for a pandemic has meant that when it occurred, we didn&apos;t have to sit down and say &apos;Let&apos;s talk about the flu. Here&apos;s the things you need to look out for with flu,&apos; &quot; he said.&lt;a name=&quot;heat&quot;&gt;&lt;/a&gt;
              &lt;p&gt; 
              &lt;p&gt;&lt;h3&gt;Plenty of heat but little light so far&lt;/h3&gt;
              &lt;p&gt; 
              &lt;p&gt;Indeed, after a week of nonstop flu news, it is startling to realize that so much remains unknown. Researchers still don&apos;t have a clear handle on:
              &lt;p&gt; 
              &lt;ul&gt;
                &lt;li&gt;The virulence of the virus. While many deaths have been reported in Mexico, most cases outside that country have been mild.
                &lt;li&gt;The symptoms. What is killing people in Mexico and why aren&apos;t there more deaths outside that country?
                &lt;li&gt;The attack rate. The so-called r-zero of a pathogen is a measure of how easily it spreads in a susceptible population. If the r-zero of a bug is below one, it will quickly burn itself out. Measles and chickenpox typically have an r-zero of about 10; the seasonal flu is about 1.5.
                &lt;li&gt;The denominator. A few dozen deaths out of a few thousand cases is very worrisome. But the same number is much less scary if there are hundreds of thousands of cases.
                &lt;li&gt;The origin of the virus. Although this strain of A (H1N1) is derived from swine flu, there is no evidence that pigs anywhere have been infected by it. In fact, both CDC and WHO have stopped referring to its porcine antecedents altogether.
              &lt;/ul&gt;
              &lt;p&gt; 
              &lt;p&gt;&quot;This is really soon to have as much information as we have, but it&apos;s frustrating because those are the pieces we really need to understand this better,&quot; Dr. Nichols said.
              &lt;p&gt; 
              &lt;p&gt;One explanation of the different patterns of disease in Mexico and elsewhere, she said, might be that the virus has evolved to be less virulent as it passed through humans.
              &lt;p&gt; 
              &lt;p&gt;In that model, the virus would have caused more serious disease among early Mexican patients, but would be milder among tourists who were presumably infected at some remove from the first cases.
              &lt;p&gt; 
              &lt;p&gt;Studying the virus as it changes over the next few months may be able to rule that model in or out, she said.&lt;a name=&quot;mild&quot;&gt;&lt;/a&gt;
              &lt;p&gt; 
              &lt;p&gt;&lt;h3&gt;Most Mexican Cases Could Be Mild&lt;/h3&gt;
              &lt;p&gt; 
              &lt;p&gt;A possibly overlapping explanation, Dr. Low said, is that there are actually hundreds of thousands of cases in Mexico -- but most of them are so mild people don&apos;t even stay home from work.
              &lt;p&gt; 
              &lt;p&gt;In this model, tourism workers throughout the country would inadvertently infect their customers - and tourists who have visited all parts of the country have come back with disease.
              &lt;p&gt; 
              &lt;p&gt;The serious cases and deaths then would just be the proverbial tip of the iceberg.
              &lt;p&gt; 
              &lt;p&gt;The problem right now is &quot;we really don&apos;t have a good sense of the denominators in Mexico,&quot; according to Tim Brewer, M.D., of McGill University in Montreal.  
              &lt;p&gt; 
              &lt;p&gt;Until those numbers are verified, it will be difficult to get the big picture of the outbreak.&lt;a name=&quot;evolution&quot;&gt;&lt;/a&gt;
              &lt;p&gt; 
              &lt;p&gt;&lt;h3&gt;Unprecedented Look at Viral Evolution in Action&lt;/h3&gt;
              &lt;p&gt; 
              &lt;p&gt;&quot;Trying to understand why we&apos;re seeing a different picture in Mexico than here is really the critical question,&quot; Dr. Besser said.
              &lt;p&gt; 
              &lt;p&gt;He said the agency has set up a new rapid test lab in Mexico City that will help to broaden the picture of death and disease.
              &lt;p&gt; 
              &lt;p&gt;Dr. Nichols, looking forward to data generated by that lab and others, said this is a golden opportunity for flu researchers -- the first time they&apos;ve been able to watch the evolution of a new human strain almost from the beginning, she said.
              &lt;p&gt; 
              &lt;p&gt;&quot;I can tell you a lot about influenza virulence in chickens,&quot; Dr. Nichols said, but much less is known about what causes flu virulence in people. 
              &lt;p&gt; 
              &lt;p&gt;New molecular research tools, applied to the H1N1 outbreak, should allow researchers like her &quot;to really pinpoint what are the determinants in a virus like this that cause severe disease,&quot; she said.
              &lt;p&gt; 
              &lt;p&gt;There is already some evidence that the virus is changing, Dr. Low said. 
              &lt;p&gt; 
              &lt;p&gt;Researchers have documented a seven base-pair in the gene for neuraminidase - the &apos;N&apos; in H1N1 -- although what that means is not clear.
              &lt;p&gt; 
              &lt;p&gt;This virus appears to be the result of a so-called &quot;antigenic shift&quot; -- a mixture of genes from several different strains that just happened to find themselves in the same host and swapped genetic material.&lt;a name=&quot;worrisome&quot;&gt;&lt;/a&gt;
              &lt;p&gt; 
              &lt;p&gt;&lt;h3&gt;Lack of Immunity Makes This Virus Worrisome&lt;/h3&gt;
              &lt;p&gt; 
              &lt;p&gt;Researchers don&apos;t agree on the details. Some, like Dr. Nichols, think the strain shows signs of swine, human, and avian flu, although others are now suggesting it&apos;s a mixture of two types of swine flu.
              &lt;p&gt; 
              &lt;p&gt;Either way, we don&apos;t have a &quot;baseline immunity&quot; to it, Dr. Brewer said.
              &lt;p&gt; 
              &lt;p&gt;Lack of baseline immunity is one reason why experts have been concerned about the H5N1 avian flu. Although it&apos;s highly dangerous, H5N1 is rarely able to infect humans -- but it might undergo such a shift and gain the ability to transmit easily among people.
              &lt;p&gt; 
              &lt;p&gt;Although scientists for years believed that the &quot;Spanish Flu&quot; pandemic of 1918 was caused by a swine flu, recent evidence indicates that it was an avian flu that underwent antigenic shift and found a world of humans with no immunity.
              &lt;p&gt; 
              &lt;p&gt;Several times this week, experts have brought up a disquieting element of that deadly pandemic, which killed more than 500,000 Americans and at least 20 million people worldwide.
              &lt;p&gt; 
              &lt;p&gt;In that case, the flu appeared in a relatively mild form in the spring -- as the current H1N1 strain has -- and then went away, only to reappear in the fall with full and deadly force.
              &lt;p&gt; 
              &lt;p&gt;That pattern could certainly recur, Dr. Nichols said, although she pointed out that the first round of the 1918 flu wasn&apos;t all that innocuous: it just seemed mild compared to what followed.
              &lt;p&gt; 
              &lt;p&gt;But there&apos;s no way to predict what will happen, she said.
              &lt;p&gt; 
              &lt;p&gt;Even if the virus does rebound, it may not be as deadly as the 1918 pandemic. Back then, even the idea of a virus was unknown. Now we have vaccines, antiviral drugs, sophisticated disease surveillance, improved supportive care, and a range of other tools.&lt;a name=&quot;severity&quot;&gt;&lt;/a&gt;
              &lt;p&gt; 
              &lt;p&gt;&lt;h3&gt;Pandemic Scale Rates Disease Severity&lt;/h3&gt;
              &lt;p&gt; 
              &lt;p&gt;The virus itself may not be as harmful as some fear, either.
              &lt;p&gt; 
              &lt;p&gt;Dr. Low said he wouldn&apos;t be surprised if it stayed low on the CDC&apos;s five-point pandemic severity scale. That scale, proposed in 2007, is not the same as WHO&apos;s pandemic threat level, which measures how quickly and widely a virus spreads.
              &lt;p&gt; 
              &lt;p&gt;Instead, CDC rates pandemics in much the same way meteorologists judge hurricanes.
              &lt;p&gt; 
              &lt;p&gt;The key factor is the ratio of reported cases to deaths. A category 1 pandemic would have a case-fatality ratio of less then 0.1%, which is about the same rate as a normal flu season.
              &lt;p&gt; 
              &lt;p&gt;Category 5, on the other hand, applies to pandemics with a case-fatality ratio of greater than 2%. The deadly 1918 pandemic had an estimated 2.5% death rate.
              &lt;p&gt; 
              &lt;p&gt;While the future of the current outbreak remains unclear, the ceaseless barrage of flu news has both informed the public -- and inflamed its fears.
              &lt;p&gt; 
              &lt;p&gt;&quot;I think some people are scared,&quot; Dr. Brewer said. 
              &lt;p&gt; 
              &lt;p&gt;Dr. Nichols said she has received calls from physicians asking whether they should stockpile the antiviral drug oseltamivir (Tamiflu). On the other hand, Dr. Low -- in Toronto, where memories of SARS are still strong -- said there&apos;s no obvious sign of panic. 
              &lt;p&gt; 
              &lt;p&gt;&quot;We&apos;ve been through this exercise,&quot; he said.
              &lt;p&gt;
              &lt;p&gt;&lt;a href=&quot;http://www.medpagetoday.com/InfectiousDisease/SwineFlu/&quot; title=&quot;Swine Flu Coverage&quot;&gt;&lt;img src=&quot;/images/swine.jpg&quot; border=&quot;0&quot;&gt;
            
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