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Press Briefing Transcript

CDC Telebriefing: Influenza Activity Update

Friday, February 23, 2012 at 1PM ET

OPERATOR: Welcome, Thank you all for standing by, at this time, all participants are on listen-only mode, during the questions  and answer session, you may press star 1 to ask a question. Today’s conference is being recorded. At this time, I will return the call over to Glen Nowak.

GLEN NOWAK: Well, thank you, and thank you all for calling in this afternoon for this CDC Update on influenza and where we stand in the current influenza season. This telebriefing is going to be handled by Dr. Joseph Bresee. His last name is B-R-E-S-E-E. He's an M.D. and Chief of our Epidemiology Prevention Branch at the CDC’s Influenza Division. He'll start with opening remarks and then we'll turn it over to questions and answers. So I will now turn it over to Dr. Bresee.

JOSEPH BRESEE: Good Afternoon, everybody. I'm going to start with a couple of summary statements about what we are seeing in the season so far. Then I’m going to questions and answers and have answers to any question you have.  So today's CDC published a summary of influenza activity in the U.S. It brings us up to date so far in the season and also the information in the report covers the season through February 11. In addition, this week's Flu View on the website reports an update on influenza activity for the week of February 12 to 18, 2012. So, I want to take a few minutes to describe what we have seen so far this season.

First and most important, the flu season has officially begun. This week's flu review reports that the national percentage of respiratory specimens testing positive for influenza rose to 14.4 percent from 13.4 percent the prior week. This is the third consecutive week this season that the percent of respiratory specimen testing positive for flu has surpassed 10 percent which is generally a marker to indicate the flu season has begun. By this measure, activity this season is off to a very late start. In fact, this is the latest start to the flu season in 29 years. Based on CDC flu surveillance data the percentage of respiratory samples testing positive for flu has remained below the 10 percent mark until February only once before. This occurred during the 1987-88 season. Despite activity remaining low in the U.S from early October through January, influenza viruses have been reported from all 50 states. Influenza A, H3N2 viruses, 2009 Influenza A H1N1 viruses and Influenza B viruses have all been identified this season in the U.S.

So far influenza A H3N2 viruses have predominated, accounting for more than 70 percent of viruses that have been typed. The majority of influenza viruses characterized so far this season are well matched to the strains in the 2011-2012 influenza vaccine. Although, slightly fewer than 50 percent of the flu B viruses tested this season have been similar to the Influenza B component in the 11-12 influenza vaccine. Very few B viruses have circulated in the U.S. so far this season.  Testing of U.S. viruses this year show all are susceptible to the antiviral drugs Oseltamivir and Zanamivir and these data reinforce the value of antiviral medications, especially for those with serious illness and those at higher risk for serious illness due to influenza because of underlying health condition. Unfortunately, because influenza activity has been relatively low so far this season, levels of severe influenza have also been low. Hospitalization rates for patients with laboratory confirmed influenza remain low. Pneumonia and influenza-related mortality based on our 122 cities mortality reporting system hasn't exceeded the epidemic threshold for more than a week and continues to remain low and three influenza pediatric deaths have been reported this far this season compared with 122 such deaths reported last season. In fact, since 2004 when pediatric deaths associated with influenza infection became a nationally notifiable condition the number of deaths reported to the CDC each year has ranged from 46 in the 2005-06 season to 282 deaths in the 2009-10 season. In fact, 340 influenza associated deaths among children were reported to the CDC during the 2009 H1 pandemic.

While most indicators of seasonal flu activity are currently low we expect them to increase in the coming weeks. For instance, visits to doctors for influenza-like illness nationally remain below baseline this week,  but two of the ten  U.S. regions representing mid-western states reported ILI activity above region specific baselines and increased from one last week. Also, two states report widespread influenza activity this week and increased from one from last week. Regional influenza activity was reported in 13 states and increased from 12 last week. And 20 states reported local influenza activity and increased from 17 last week. Only the U.S. Virgin Islands and Guam reported no influenza activity this week. This information and a lot of other information is available on the CDC’s Flu View and the past issues are archived for you to see on the CDC website.

To summarize, the United States is experiencing a late start to influenza season this year, but activity has increased in the past few weeks. This pattern is unusual but not unprecedented. Although, we could attempt to speculate as to the possible reasons for the late start, we can only be certain that flu is inherently unpredictable. In addition to flu season starting late, they can also reach peak activity late. In fact, in the past 35 seasons we have seen peak activity as measured by the month with the highest percentage of respiratory specimens that test positive for flu four times in March and two times in April. So we can't predict the timing of peak activity in the United States nor when the season will end, nor can we predict how severe the season will ultimately be. So if you haven't gotten the flu vaccine yet or your loved ones haven't gotten theirs yet, get your vaccine now. It's not too late. Flu vaccine remains the best way to protect yourself from getting the flu. You will need this season's vaccine to protect against this season's influenza.

JOSEPH BRESEE: As you know CDC recommends everyone 6 months of age and older get the annual flu vaccine. Before I finish let me update you on one little bit of data that just came in over the last couple of days. As you, know yesterday the World Health Organization (WHO) announced its recommendations for three vaccine viruses to be included in the trivalent northern hemisphere flu vaccine for next season, 2012-13 season. The recommendations for both H3N2 component and the B component of the vaccine have been updated this year.  WHO's recommendations to update two of the three strains for next seasons vaccine was based on data collected on influenza viruses circulating in countries around the world, but remember the current 2011-12 vaccine remains a good match to influenza viruses circulating in the United States at this time. Finally, as an option for vaccine manufacturers that would like to create a quadrivalent vaccine or a four component vaccine that would protect against four different viruses, WHO has also recommended a second B strain. Production of a quadrivalent vaccine has been under consideration for some time mostly because there are two very different lineages of B viruses called the Yamagata and Victoria. Selecting the B virus component for the vaccine has been challenging because the circulation of these two lineage viruses have been unpredictable and they often Co-circulate. At the end of this month the vaccine viruses in the U.S. will be chosen at the FDA’s VERPAC meeting in Washington, D. C.  An optional fourth vaccine component doesn't necessarily mean a four component vaccine will be available immediately, however. Finally, implementation will depend on manufacturers and this could take some time. It does however; signal that we are moving in the direction of a quadrivalent influenza vaccine. That's all I have. I'm happy to take questions from anybody who has them.

OPERATOR:  At this time we are ready to begin the question and answer session. If you would like to ask a question, please press star one. You will be prompted to record your name. To withdraw your request you may press star two. Again press star one to ask a question and one moment for our first question. Our first question come from Daniel DeNoon with WebMD, you may ask your question.

DANIEL DENOON: Thanks for taking my question. Do you have figures on the up take of flu vaccine this year and is there any sense that the larger numbers of flu vaccinations have had any effect on the number of infections this year?

JOSEPH BRESEE: Great question, Daniel, thank you so much for the question. We do have some information. So far what we know is 132 Million doses of vaccine have been distributed in the United States. While we don't know the total coverage at this point in time we do know that as of November or so there were more people vaccinated by November this year, then where vaccinated by November of last year. But the second part of the question is actually quite interesting. I do think, in fact, that as vaccine coverage increases we ought to see less disease in the United States. So I think although this season has been mild and the onset has been late and that can’t be attributed solely to vaccine practices I do think increasing vaccine coverage in the United States will certainly and probably is certainly playing a role in less transmission and less disease this year.

GLEN NOWAK:  Operator, next question.

OPERATOR: Our next question comes from Donald McNeil with the New York Times. You may ask your question.

DONALD MCNEIL: Hi, Joseph. Can you talk a little about why this season is so odd? Why the H3N2 predominating and so little H1N1? Is that a result of people having been exposed to the pandemic H1N1 earlier? And can you talk a little bit about what's going on in the rest of the world and how it may affect the United States? I have noticed the B virus seems overwhelming in China and parts of Southeast Asia which seems unusual.

JOSEPH BRESEE: Don, thanks for those questions, they are good questions. I wish I knew the right answer to both of them. Let me give you a shot. First, the reason this season is late and mild and we see H3N2 predominating is probably related to a bunch of different factors. Some of which we know and some of which we don't know. First what we know is the timing of influenza and how severe it is each year and which viruses circulate are highly variable and hard to predict. But there are three things that are interesting. One is the fact that the virus is circulating this year are quite similar to the viruses that circulated last year. So it's possible that in the population there are higher levels of immunity to these viruses compared to last year and that may mean less transmission and less disease. Second what we know and as I said the vaccine coverage rates continue to trend upward. That should lead to less transmission over time and less severe disease over time, especially if high risk people continue to get vaccinated in higher numbers. Those things I know. And are probably related, probably aren't the sole explanation for what we are seeing this year.  I think there are probably high levels of antibodies in the population against pandemic H1N1 because of the high levels of disease in 2009 and 2010. That probably play as role in the amount of H1 disease we are seeing this year.

Finally, I have been asked about the weather. Does the weather play a role and the weather might. There's been intense research on weather and how it relates to respiratory virus spread. We do know that in cold, less humid times influenza viruses remain more viable for longer.  We know that in cold weather people tend to cluster inside more and maybe facilitate transmission. We know those things, how those things impact this season and what total impact they have on flu circulation overall I don't know. But I think they might play a role here as well. So I think in the U.S. we are seeing a pattern. We have seen it before occasionally, but it's not very common. Probably related to a bunch of factors, some of which we can speculate on and some of which we can't. I do think that globally it gets even more complicated. In China and northern Vietnam, Laos, Cambodia, we are seeing lots of B’s right now. In fact in Laos we are seeing lots of H1’s as well, and in Mexico we are seeing more H1’s than in the U.S.  The specific patterns of influenza virus circulation around the World, I find difficult to predict. Luckily they are smart people in the world that can predict it well enough to make a good vaccine each year. But I'm not sure I can add much more to that. Thanks.

GLEN NOWAK: Operator next question.

OPERATOR: The next question is from Mitchell Zoler with Internal Medicine News.

MITCHELL ZOLER: I wanted you to put the 132 million doses of seasonal vaccine distributed in some kind of better context. I know that outside of a pandemic the CDC isn't really responsible for the distribution. How does that compare to perhaps any kind of goal or sense you have of what would be adequate levels of immunization in the country?

JOSEPH BRESEE: It's a great question. I will clarify one thing. As you know, the doses distributed don't mean doses given. CDC measures two things. Early in the season we measure how many doses have been sent out to folks. We don't know how many have been given necessarily. So we do surveys to measure how many actually were given to a human. Therefore estimates what the uptake is in different populations. I think the 132 million doses distributed so far this season is about on par with what we have seen the last few years. Slightly under what was distributed all of last season but we're not quite finished yet. I don't know what will happen by the end of the season. I think coverage rates in key populations like pregnant women and children have been trending upwards steadily- slowly but steadily over the last couple of years. That's gratifying.

I think that our goals for influenza vaccine coverage are much higher than they are now in most groups. We'd like to get to 80 percent coverage in high risk groups for instance. We are not near there in any group. More people need to get flu vaccine than currently do. We think by doing that we can decrease both the transmission of influenza and therefore protect people who didn't get their vaccine this year but more importantly protect those people who did get the vaccine.

GLEN NOWAK: Next question.

OPERATOR: The next question is from Theresa Juva with the Journal News. You may ask your question.

THERESA JUVA: Hi. Thanks for taking my question. Why is it that some regions are showing more activity than others? There are widespread cases in Colorado and California and other places it's still sporadic. Why is that? Is there historical pattern to where you see cases?

JOSEPH BRESEE: That's a good question. There is not a historical pattern at least within the United States borders. Globally clearly there are patterns where the northern hemisphere sees disease mostly in the winter time and the southern hemisphere in the summer time. Within the United States each year where flu shows up first, where it occurs next and where it finishes is pretty variable and entirely hard to predict. That's why each season- because we can't predict well where it will show up first and where it will go next- we recommend that everybody get the vaccine before influenza activity starts in the U.S. anywhere. So we make sure folks are vaccinated well ahead of the season. Thanks.

OPERATOR: Again, if you have a question press star one. Our next question is from Michael Smith with MedPage Today. You may ask your question.

MICHAEL SMITH: Thank you, Dr. Bresee. A small technical question. I thought I heard you say that the proportion of ILI that was actually positive for flu was 13.4 in the week ending February 11 and 14.4 this week or the most recent week. I'm curious because MMWR says 15 percent for the week ending February 11.

JOSEPH BRESEE: You have a good eye. I will check on the numbers after the call. What happens sometimes is we continue to update the numbers from past weeks with this week's data. So we get some late reports from labs and we'll continue to update. What you will see is in past weeks in the Flu View reports that some of the numbers will change over time. Not dramatically usually, but slightly.

GLEN NOWAK: Next question.

OPERATOR: At this time I show no further questions. If you would like to ask a question press star one at this time.

GLEN NOWAK: All right. If there are no further questions we will end this press briefing. We'll post the transcript as soon as we can. Probably sometime later this afternoon. If people still have questions related to seasonal flu the best way to get them answered is to call the CDC press number which is 404-639-3286. Thank you.

OPERATOR: Thank you. This does conclude today's conference. At this time you may disconnect your line.

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