Press Briefing Transcripts

CDC Telebriefing on Investigation of Human Cases of H1N1 Flu

May 21, 2009, 12 noon ET

• Audio recording (MPEG)

Operator: Welcome and thank you for standing by.  During the question and answer session today you can press star 1 to ask a question.  Today's conference is being recorded.  At this time I’ll turn the call over to Mr. Glen Nowak, you may begin, sir.

Glen Nowak: Thank you.  Thank you all for calling in this morning for the update on the novel H1N1 virus. I am joined by Dr. Anne Schuchat, who is Director of CDC’s National Center for Immunization and Respiratory Diseases and Dr. Schuchat will provide brief opening remarks and she will take your questions.  So, I will turn the phone over to Dr. Anne Schuchat. 

Anne Schuchat: This afternoon what I would like to do is to continue to put what we're seeing into perspective for you and give you a little bit of an update on a report that is in today’s Morbidity and Mortality Weekly Report about some interesting laboratory studies that have just been completed. 

The novel H1N1 virus continues to circulate in the U.S.  Remember, this is a new virus.  So far it appears to be behaving fairly similarly with the seasonal flu viruses, but it's new and we're still making sure that we understand it going forward.  We know that seasonal flu viruses cause a lot of illness each year in the U.S. and that even with seasonal influenza things can be unpredictable.  So we do think that the H1N1 new strain is very likely to be unpredictable and we're keeping an open mind to what will happen as things go forward.  We are seeing activity decline in some areas, but we're seeing increased or localized outbreaks in other areas and so we should expect to see more cases, more hospitalizations and potentially more deaths as we move into the weeks and months ahead.

The study that CDC is reporting today in our MMWR suggests that older adults might have some pre-existing antibody against this new H1N1 strain, but we don't know yet what that will mean in terms of actual immunity or clinical protection.  It's interesting that the laboratory findings we're reporting seem to correlate with the epidemiologic data that we have so far that suggests most of the illnesses we're seeing have occurred in younger people and have spared the elderly who are at great risk for seasonal influenza. 

As I mentioned, there are localized outbreaks going on in several states, and I think there's been substantial attention to New York City and surrounding areas where there have been increased levels of this novel H1N1 influenza or increased levels of influenza-like illness.  There have been some school dismissals in the New York City area and in other parts of the country and those are being carried out in general, consistent with our national guidance that when there's high absentee rates or high illness in students or staff and the school can't really function, it's appropriate to dismiss students. 

I want to talk for a couple of minutes about the MMWR article which is entitled “Cross-Reactive Serum Antibody Response to a Novel Influenza A (H1N1) Virus After Vaccination with Seasonal Influenza Vaccine.”  This is a report of studies that were carried out here at the CDC laboratory and we had great cooperation from NIH and from academic researchers and others, the manufacturing companies, in providing serum that had been studied in vaccine trials so that our laboratory scientists could learn as much as we can about how this new virus might behave when it's exposed to antibodies to the seasonal flu vaccine.  So this is a laboratory study, not a clinical or epidemiologic study, and it came about through a great partnership across government and academia.  Our MMWR Today report provides details of a serology study of samples from children, younger adults and older adults who were vaccinated with the recent seasonal influenza vaccine to try to understand whether those seasonal vaccines offered any immune benefits against this novel H1N1 flu.  Serology means that we're studying blood or serum to identify antibodies in the actual serum.  The presence of the antibodies can indicate immune protection, but it's an indirect measure.  So these studies are just interesting and not definitive. 

The results presented in the study found that the seasonal influenza vaccine provides little or no immune benefit against this novel H1N1 flu virus.  The bottom line of the study is that adults might have some degree of preexisting cross-reactive antibody to the novel H1N1 flu virus, especially older adults, over 60 or over 65 depending on the samples that we had.  However, we don't know if those antibodies that we saw provide any protection against the novel influenza A in actual people.  The presence of preexisting antibody may be due to previous exposure through infection or vaccination to an Influenza A H1N1 virus that more closely related to this novel H1N1 flu virus than the contemporary seasonal H1N1 strains that we have.  CDC does not believe that seasonal influenza vaccine would provide any meaningful protection against this novel H1N1 strain.  On the other hand, we do believe that seasonal flu vaccine is important and can help protect people from the regular flu viruses that circulate each year.  So this is a fairly complex study and we'll be happy to answer questions when I finish the formal opening here. 

I want to remind you that vaccines are a very important part of our response to flu, including novel influenza that may become pandemic.  CDC has isolated the novel H1N1 virus and we're working to make a candidate vaccine virus provided to industry so manufacturers can scale out for production if necessary.  We remain hopeful that we will have vaccine viruses to send to manufacturers at the end of May, and that's still within the original timelines that we have been describing.  Remember there are many steps involved with producing a vaccine.  We're committed to work across the government with NIH, FDA, BARTA and the manufacturers of flu vaccine to see further about developing full-scale vaccine production. But remember, this is all unpredictable, just like the seasonal flu vaccine production, the steps involved are subject to variation of the strains, of the manufacturing process, et cetera.  If things go well and we do move forward with full-scale production, it would still be several months before a vaccine against this new virus would be available.  The seasonal flu vaccine production efforts are ongoing.  They remain on track according to what we heard from the manufacturers and we are expecting to have a full and aggressive seasonal flu vaccine campaign next fall.  Remember that seasonal flu does cause about 36,000 deaths each year and 200,000 flu-related hospitalizations in the U.S. each year.  So while we have a lot of uncertainty about this new H1N1 virus and the steps involved with vaccine production, we continue to be certain that seasonal flu vaccine in the fall would be a good idea for people to lower their risk of regular flu. 

In closing, I really want to make sure that you know we think continued vigilance is important.  As we are seeing in our state reports and in trends and certain communities, this outbreak is far from over here in the United States.  Because infections have occurred mainly in younger people so far, we think that older adults might possibly have protection that might help ward off this infection from the novel H1N1 virus.  The study we're reporting today provides a little clue consistent with that clinical observation we've made.  We still recommend vaccination with seasonal flu vaccine and we are looking aggressively at the steps involved with vaccine development.  Remember that it's still too early to predict how severe this particular H1N1 outbreak will turn out to be in terms of illness or death or spread, but we're aggressively responding with public health partners here and working together with our international colleagues.  Our extensive efforts on the monitoring and science front are continuing with our goal being to learn as much as possible, as fast as possible, so that we can use it in our control efforts.  This is an ongoing public health threat and we're continuing to be aggressive.  So I would welcome the questions that you have. 

Glen Nowak: Operator, we'll take the first question. 

Operator: Thank you.  Our first question comes from Shahreen Adedin from CNN.  You may ask your question. 

Shahreen Abedin: Yes, Hi.  Thank you for taking my call.  I'm wondering, can you give us a further breakdown of the numbers of younger versus older cases, older people, the ages and as far as the cases that you've seen of this new virus?  And you said there's a downturn only in some areas and not in others and could you tell us where that downturn is.  My second question is about --would you -- are you expecting very soon, are there certain front-runners of people who are sending you useful forms of vaccines that you think that are coming out there.  I understand Dr. Boucher may be sending you one today.  Do you have any news on that front? 

Anne Schuchat: Okay.  Let me take the first one or two questions to make sure I get the train of thought. 

Shahreen Abedin: Sure. 

Anne Schuchat:  Of the cases that we have reported to us which have gone under some type of laboratory testing, 64 percent of those are occurring in people between 5 and 24 years of age.  Just about 1 percent of our cases are in people over 65 so the vast majority are in younger persons and the biggest proportion of those are in people in the 5 to 24-year-old age group.  Your second question was about what we're seeing geographically.  At the national level, we're seeing that the percent of visits for influenza-like illness is starting to turn down.  This is an aggregate of the whole country, but that's a good sign.  It is consistent with the idea that on average, the worst may be over.  On the other hand, in our New England region, we're still seeing an upsurge in influenza-like illness in the New Jersey-New York area we're still seeing an upsurge.  The mid Atlantic area is seeing a decline.  The southeast area is somewhat seeing a decline, but it may be too soon to say about that and the Midwest and southwest are also starting to see declines.  This is one of those issues where we really need to keep our eyes out.  You know in New York City things looked like they were getting a little better and then it looked like they were getting worse.  With the new virus, it may take some time for it to pass through communities, but in terms of the way that we're trying to track this at the national level, we think that it's an ongoing concern.  We also, on our website have a map.  You can find it under the spotlight for H1N1 disease, and each of the states rates the condition of what’s going on in their state and that's a really good thing for you to look at, particularly if you're reporting locally. 

States that are having widespread disease are defined as ones where more than half of the regions in the state are seeing increases in the influenza-like illness and even in some of the states that aren't seeing that kind of widespread disease, they have localized outbreaks that are quite important.  So this is the long answer to the geographic question, and I think the most important thing for people to realize is that the  virus is spreading in many areas and it's variable.  Your public health support at the local and state area are working very hard to make sure they know what's going on and to issue local guidance.  We're supporting them from the national level, but just like weather, this is a local occurrence and people need to stay in tune with what's going on with their own communities and the local health authorities will have the best information.  Can we go to the next question? 

Operator: The next question is from Maggie Fox of Reuters.  You may ask your question.

Maggie Fox: Dr. Schuchat, can you update us a little bit on the epidemiology?  Do you have any kind of estimates on total cases?  We've been using the 100,000 that Dr. Besser gave us last week, and can you -- well, no, that's my main question.  Thanks. 

Anne Schuchat:  Yeah.  Let me give you the cases that we're counting and what our estimate is on that.  Here in the U.S. we now have 5,764 probable and confirmed cases.  As we've been saying, we think that's a vast underestimate and that 100,000 figure that you heard about a few days ago- that came from an estimate that perhaps one in 20 of the total cases that were occurring might be the ones that we know about from these lab testings.  It's just an approximation.  I think if you heard 100,000 a couple of days ago, we're at a higher number now, but really what we're trying to do is follow these local trends.  With seasonal influenza we don't count every single case.  We use modeling at the end of the season to do some estimates based on hospitalizations and deaths and influenza-like illness and it's with some sort of quick math, looking at our seasonal flu patterns and then trying to assess what's going on here that some of our scientists came up with the 100,000 estimate.  It's not the kind of estimate that we're going to be updating on a daily basis.  Next question, operator. 

Operator: Our next question comes from Mike Stobbe from AP. You may ask your question. 

Mike Stobbe: Hi, thanks for taking the call.  Doctor, first you said there was regional variation and you talked about it in terms of visits.  Visits to what?  Did you mean to emergency rooms and doctor's offices?  Also, I wanted to ask in the MMWR- that's based on 80 children and 280 adults, is that right?  Are those all U.S. people and lastly, I'd like to ask if you can describe in plainer terms than you did the antibodies that were found in that and what they do or don't mean.  I'd just like a little more information to be clear. 

Anne Schuchat:  Yes.  Let me give you some answers and then we might have Dr. Jackie Katz provide a little bit more.  The first thing to say is that these samples came from the manufacturers, from NIH researchers and from others and they're actually mostly --they're not just Americans they do include Europeans where some of these vaccine studies were made.  In terms of the numbers, it varies by age group.  I guess I can go through all of the numbers, but there were 33 children.  It's probably too many for me to go through.  The MMWR is actually on the Web site right now so you'd be able to get the numbers together.  So it's 79 children. 

Is that all you were asking about was the children?  Basically it's just based on 79 children.  A larger number of adults were in the study.  I think the important thing to say is that these are interesting results.  They tend to be consistent with what we're seeing on the epidemiologic front, but the laboratory tests that we use to measure the antibody is not a traditional one that we can easily correlate with clinical protection.  We had to use a different acate and so we make some assumptions about what that might mean, but we need to be very cautious.  We were not using the traditional way of measuring antibody against influenza virus for this particular asset.  But I think the important feature is that we saw a difference in pre-existing antibody levels in seniors which seems to correlate with what we're seeing with the epidemiology of this infection.  Whether it will pan out over time, the seniors really don't get this infection, we can't say.  Whether this particular acate will pan out over time as predictive of clinical protection, we can't say.  But we thought it was important to get this information out into the community of researchers and others quickly.  This was a cross reactive micro neutralization antibody, not our typical acate and so it just needs to be taken with caution. 

Glen Nowak: Mike, did that answer your question? 

Operator: One moment, please.  Mike, your line is open. 

Mike Stobbe: Thanks.  I guess -- could you also clarify the visit that you talked about?  Was that to hospital emergency rooms or --

Anne Schuchat:  Yes, thank you.  That other question I'll give you an easier answer for.  We have systems to monitor office visits through our influenza-like illness surveillance or ILInet but we're also looking at emergency department visits through something called BioSense, and both of those systems are showing regional variation - things on the upswing and things on the downswing in different communities.  We have also seen data that's been collected by some of the bigger cities that have emergency department or other syndromic surveillance systems and similar to the systems that we're tracking nationally, those specific cities are also finding variability.  So I think that we have been tracking this disease through the virologic surveillance, through the ILInet, through emergency department visits. We are also looking at pneumonia and influenza mortality from our 122 cities and the good news is that we haven't seen an increase in that metric yet.  For that we're grateful that there don't seem to be large scale increases in deaths in the United States comparing it with the seasonal baseline.  We'll be looking at hospitalization data soon, but we don't have that yet. 

Glen Nowak: Next question, operator. 

Operator: Thank you.  Our next question comes from Helen Branswell with the Canadian Press.  You may ask your question.

 
Helen Branswell: Thank you very much for taking my question.  I was wondering if we could sort of drill into the data in terms of the seniors.  It isn't actually – I mean looking at the numbers unless I'm reading them wrong.  You're not seeing cross-reactive antibodies in all seniors, it’s sort of a subset of seniors, and I'm wondering if there's any estimate or explanation as to why that is and if you're seeing that mainly in the U.S. sera versus the European sera and also I would wonder if you could sort of explain how it is if you're seeing it in 43 percent in seniors, why are only 1 percent of the cases in seniors?  Is it a combination of maybe some cross-protection and maybe patterns of exposure? 

Anne Schuchat:  About a third of the adults 60 years of age and older had some level of cross-reactive antibody against the novel H1N1 virus before they were vaccinated in this study.  Important to remember is we're not talking about thousands of specimens.  We're talking about a relatively small number of specimens.  The seniors that we studied were from the United States and not from Europe.  The issue of -- you know, there are so many steps removed here.  We have clinical findings on this novel H1N1 virus at one point in time.  Today less than 1 percent of all of the cases we have laboratory results on are coming from people 65 and over.  Will that increase over time? We've been saying in these briefings over the past several days, we think virus is initially amplifying among teenagers in schools or among college students coming back from spring break and mixing and more seniors might get infected over time as the strain circulates deeper and deeper into our community.  The next thing that's a step removed is that this is a laboratory test that's not even the standard test that we use against influenza viruses.  So we have to make inferences.  A third issue is the size of the sample that is not enormous and so the uncertainty around that would be great.  So I don't think it's at all surprising that we have one-third in the lab study and 1 percent at one point in time in the epidemiologic data and it's just one of the frustrating features of the influenza that we don't know as much as we want to know today and hopefully over the time to come we'll learn more and more. 

Glen Nowak: Next question, operator? 

Operator: Next question comes from Daniel DeNoon from WebMD.  You may ask your question. 

Dan DeNoon: Thank you very much.  Another frustrating feature of influenza I hear from clinicians seems to be that the rapid flu test is not as sensitive as it's cracked up to be.  The label suggests 70 percent sensitivity.  It seems that experience is less than that.  Can you talk about the sensitivity of the rapid test for both the seasonal and for the novel H1N1 and what getting a flu test means on the level of someone with a influenza-life illness who goes to see a doctor? 

Anne Schuchat:  You know, we wish we had better tests for influenza.  Much of the preparedness effort that we have had has been focused on diagnostic test development to get better tests against new strains and technologies that would be even better against the regular flu strains. And of course it's through some of that research that we found the first case of the United States of this virus.  There are rapid tests out there and their label sensitivity is sometimes described as overestimating what clinicians see in real practice and of course, that is frustrating for providers.  There are many things that can lead to variation in the sensitivity of a test against influenza.  One possible variation is the strains that are circulating.  When the tests are licensed they tested against a lot of influenza strains, but as years change, things drift a bit and the sensitivity may vary depending on which particular seasonal flu strains are circulating.  The sensitivity of the test also can vary with the age of the patient.  The tests seem to be more sensitive in younger children than in adults, perhaps because of the amount of virus that young children are shedding.  A third variable is the swabber.  It turns out that some people are better at collecting a specimen than others and for many laboratory tests in clinical medicine, the specimen collection is just as important as the actual laboratory reagents or the way the test is performed in the lab.

Interestingly enough, we believe in some of the early results that we have right now that some of the rapid tests out there may perform a little bit better against this novel H1N1 strain, than against the seasonal A strains that are circulating.  This isn't something that we have great numbers behind, but it is an observation that has been coming in.  If it's true, when we actually are able to confirm that observation, it could have something to do with a higher viral load or a higher amount of virus that's present with this novel H1N1 strain than the seasonal strain that's circulating.  Of course, even if it's a little bit more sensitive for the novel H1N1 strain, the sensitivity is not 90 percent to 100 percent.  So we are recommending that when it is important, additional tests be performed.  A positive is probably important, but a negative doesn't necessarily rule out influenza.  The way that diagnostic tests are being used, though, right now at this point in our seasonal influenza is different than might happen at other stages.  We don't think it's as important to confirm every single patient with the H1N1 novel strain.  We are trying to make sure we get test results on a sample of patients so that we can understand the trends over time.  Are things getting better or worse and certainly, when there's a new infection in a new state that doesn't even know whether they have the novel H1N1 virus, we're trying to make sure they confirm the presence in the community there. 

Glen Nowak: Operator, next question? 

Operator: Thank you.  The next question is from David Brown from the Washington Post, you may ask your question. 

David Brown: Yes, thanks very much.  There seems to be a booster effect in the 18 to 64 age group where 9 percent have what appears to be a protected antibody before being vaccinated with seasonal flu but then after being vaccinated it goes up to 25 percent, and I just --if you could comment about whether and why not or why that isn't viewed as a sort of useful observation and, you know, in terms of clinical application and my other question is since the virus that reappeared, the H1N1 that reappeared in ‘77 was the same one that disappeared in '57, how do you explain this greater protection the older you get?  Do you have any sense of sort of which viruses, which years might have been the ones that were most important in terms of providing anything protection to the novel strain? 

Anne Schuchat:  You know, I think just to correct something.  I think you said something about the protective level.  We need to be very cautious in concluding that this micro neutralization antibody is protective.  We really don't know that.  So there was, as you said, a bump in the 18 to 64-year-olds, 90 percent with the titers of over 160, up to 25 percent post-vaccination.  We really don't know whether that is correlated with protection.  We look at the post-vaccination to pre-vaccination ratio with a factor of two.  That's pretty wimpy.  If you look at what happens with the seasonal flu vaccine, you can see that we're seeing ratios of 12.  So, when you have small numbers and you're looking at titers, you can see there are these little variability’s, but we don't consider that post-vaccination to pre-vaccination ratio even if it were with a protective laboratory acate to be very impressive and then here we have that additional qualification if this is a surrogate acate.  So that's really why we aren't pushing that finding.  Wouldn't it be great if there was boosting, but we don't think we have sufficient evidence of that at this point to conclude that.  You know, I would say that there will be lots more studies going on with the seasonal flu vaccine because it was used this year and we have a lot of serum that's been collected over the course of our investigation.  So these are the first results we were able to produce with the vaccine studies that were done with the seasonal flu vaccine, you know, that would basically -- with the sera that was in freezers around the world, we could get some quick results, but I think in the weeks or months ahead, we hope to have a lot more direct information that would help answer that question. 

Glen Nowak: Next question, operator? 

Operator: The next question comes from Richard Martin with the St. Petersburg Times. 
Richard Martin: Thanks for taking my call, doctor.  Can you talk a little bit more about how effective the seasonal flu vaccine is and can you speak to some of the popular arguments against getting one such as the dangers and the ingredients such as mercury, other risks and the strains in the vaccine not matching the strains that are circulating? 

Anne Schuchat:  Thank you.  Every year a new -- we've --okay.  Every year influenza vaccines are produced so every year the vaccine is different.  So when we look at the literature for influenza vaccine, an important feature is that different strains circulate and the vaccine is different.  What we know about seasonal influenza vaccine is that it works best in people with the strongest immune system and it doesn't work quite as well with the elderly and people with weaker immune systems.  That some years it works very well and some years it doesn't work as well.  The years that it doesn't work as well, we believe are related to less than optimal matches between the strains that are circulating and the strains that the vaccines were made against.  Most years the vaccine is significantly protective and can reduce illness, hospitalization and death.  There have been controversial articles written about whether the vaccine is beneficial or not and our sense at the CDC and certainly the advisory committee for immunization practices that looks at influenza vaccine recommendations every year, strongly recommend this vaccine for reducing the risk of influenza.  It's particularly important in people who have higher risk of complications of influenza and we've also recently expanded the recommendations for children all of the way up to age 18 to try to reduce illness in children and keep them healthy and in school.

There have been questions about whether influenza vaccine is safe.  There have been questions about their ingredients, you mentioned Thimerosal. Thimerosal is a preservative that’s included in vaccines that are made with multiple-dose vials in order to keep them from getting contaminated with bacteria.  Because with a multiple-dose, you can go in and out with a needle.  Thimerosal was questioned in terms of whether it might be unsafe.  There have been quite a few studies now that suggest no increased risk of long-term problems associated with Thimerosal, and we believe this is a safe ingredient of vaccines.  Last question you asked was about matches, and this is the real challenge with influenza vaccine.  Every year we do this intensive surveillance to figure out which strains are circulating and to predict which strains should be included in the vaccine that's produced each year and every year we keep our fingers crossed to see how well the prediction will work.  Unfortunately, not every year does the prediction work perfectly and so we always need to be mindful that one or more of the three influenza virus strains that are in the vaccine may not be an optimal match.  So I think that is a challenge.  I know the media has been reporting this, but some of the government's investments over the past few years have been in novel influenza vaccine production.  We would love to have an influenza vaccine that didn't have to be formulated every year.  And there is interesting research going on in that area. But so far, we still are required to use the current approach- looking at what strands are circulating, making our best prediction, and optimizing production against the strain that has been selected.

Glen Nowak: Operator, we have time for two more questions.

Operator: This question is from Richard Knox with National Public Radio.  You may ask your question.

Richard Knox: Thank you very much, Dr.  Schuchat.  I’m going to follow up with, I think, what David Brown was asking? And push it a little bit further.  Do you think at this point that the presence of some preexisting antibodies in some people might make it less likely that they need two doses of the pan-flu vaccine and thereby conserving supplies.  I realize that the pre and post-vaccine titer bump was with vaccination of the seasonal vaccine.  Is there any reason to think that there's a specific vaccine against the novel virus might be more specifically hemogenic and I have a second one if I may.

Anne Schuchat:  The question of whether two doses will be needed is a critical question.  Clearly, if some or all people don't actually need two doses, vaccines that are produced could go a lot further.  Part of the role of the NIH in clinical evaluation of vaccines is to look at the number of doses that are required.  You may recall this was done with the H5N1 vaccine studies in the past.  So it will be wonderful if some parts of the population or many parts of the population don't actually need two doses.  Our working hypothesis is that everyone who gets this vaccine is likely to need two doses, but perhaps there will be some people where pre-existing immunity will be there and one dose will lead to a primed response.  So that is definitely a great question and something we're interested in.  The best way to answer that question will be in clinical studies of a vaccine targeted against this strain in different age populations looking at response after one dose and response after two doses and those are the types of studies better planned.  You had a follow-up question.

Richard Knox: I think you just began to answer it.  I was wondering what your current thoughts regarding targeting the pandemic flu vaccine.  What are areas you're thinking about and what studies would need to be done?

Anne Schuchat: You know, there are two activities that are vital to that question.  One is the epidemiologic studies that are ongoing here in the U.S. and that will be going on in the southern hemisphere to understand who is at higher risk of this disease?  Does it affect all age groups?  Does it affect people with and without underlying diseases?  Where is the disease burden?  And that's one way that we can do our targeting.  A second factor is how does a vaccine that's produced against this virus work?  Will it work as well in different age groups with one or more dose.  So we'll be looking both at a pattern of disease that we see and then at the value that a vaccine has.  If we had a high-risk group that was clearly at risk, but really no response of the vaccine in that population, we might not want to target that population.  So those are the types of studies that we'll try to be putting together in this very complicated decision about whether anyone and everyone ought to get the vaccine that is being considered.

Glen Nowak: Last question, operator?

Operator: Thank you.  The last question comes from Beth Galvin with Fox.  You may ask your question.

Beth Galvin: Hi, Dr. Schuchat, thank you for taking my call.  I was wondering if you would talk about the hypothesis that older adults might have been exposed to a similar strain of flu, is this the ‘77 flu?  The ‘57 flu?  What are you thinking?

Anne Schuchat:  I think one possibility is that older people might have been exposed to H1N1 strains a long time ago that might have some relation to the strain we're seeing now.  Now our virologists have sequenced this virus that we’re seeing and they’ve compared it to all these other strains and this is really different.  This is not a close, genetic relative of any of the H1N1s that have been a problem in people, but the immunologic characteristics might be different than the genetic characteristics and so it would be very great if older people had been exposed to some H1N1 a long time ago that had some relationship with this one immunologically and that might lead to that pre-existing immunity they we hope is there, but we're not sure is there.  So we don't have a particular virus that we're thinking about because the genetic characteristics are so different, but we are wondering about whether there were some viruses around back in the '30s, '40s or '50s that might have been immunologically similar to the one we're seeing now.

Glen Nowak: Thank you all for your interesting participation this afternoon.  We'll be posting the transcripts on this sometime later this afternoon.  If you have additional questions don't hesitate to call CDC's Office of Media Relations.  Thank you.

Operator: This does conclude today's conference.  We thank you for your participation.  That the time you may disconnect your lines.

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U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES