Effect Measure

Summary of last year’s flu season

Posted by revere on June 30, 2008
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We started blogging on public health at the beginning of the 2004 – 2005 flu season, although we didn’t concentrate on flu immediately. We intended to use the public health problem of influenza, a disease that contributes to the death of almost 40,000 US citizens a year, as a lens through which to look at public health. The interest in bird flu and pandemic flu followed naturally. The intervening years saw seasonal influenza outbreaks that were milder than previous years, but this resourceful virus made a comeback in the flu season just concluded. CDC has just summarized the 2007 – 2008 flu season and compared it to the three previous years (1004 onward:

During the 2007–08 influenza season, influenza activity* peaked in mid-February in the United States and was associated with greater mortality and higher rates of hospitalization of children aged 0–4 years, compared with each of the previous three seasons. In the United States, influenza A (H1N1) was the predominant strain early in the season; influenza A (H3N2) viruses increased in circulation in January and predominated overall. While influenza A (H1N1), A (H3N2), and B viruses cocirculated worldwide, influenza A (H1N1) viruses were most commonly reported in Canada, Europe, and Africa, and influenza B viruses were predominant in most Asian countries. This report summarizes influenza activity in the United States and worldwide during the 2007–08 influenza season (September 30, 2007–May 17, 2008). (CDC, Morbidity and Mortality Weekly Reports)

There appeared to be two peaks if you use the proportion of visits to outpatient facilities for acute respiratory disease as a measure, one at the time of the Christmas holidays and the second in mid-February. CDC speculates the earlier peak might have been a result of fewer routine outpatient visits, thus inflating the percentage for acute illness. The later mid-February peak is more in line with previous seasons where flu reaches its height mid-February to early March. In the US, A/H1N1 predominated early in the season, but as flu cases started to pick up speed it was superseded in most regions of the US by A/H3N2 — except in the Mountain and Pacific surveillance regions, a reminder that the dynamics of this virus are complicated and still not well understood. As if to emphasize this, in Canada and Europe influenza A but A/H1N1 predominated, while in Africa and Asia there was more influenza B than influenza A. This was also true of some European countries, and even those with more influenza A than influenza B had quite high proportions of flu B compared to the US.

As previously reported, the circulating flu viruses were not a good match for this year’s flu vaccine. The match for A/H1N1 was 66%, not great but much better than the 28% match for A/H3N2. There was essentially no match for influenza B. Resistance to one or another of the two main classes of antivirals, neuriminidase inhibitors (oral form, Tamiflu, inhalable form, Relenza) and M2 inhibitors (adamantanes) showed an interesting pattern. All influenza A viruses remained sensitive to the inhalable Relenza (zanamivir) but A/H1N1 showed increased resistance to Tamiflu (oseltamivir). The proportion of H1N1 resistant increased slightly from last year, from 0.7% to 10.7%. No H3N2 were resistant to Tamiflu. But virtually all the H3N2 isolates were resistant to the adamantane class of antivirals resistance was at the same level as for Tamiflu (10.7%), but interestingly, there was no overlap, i.e., no isolate was resistant to both Tamiflu and one of the adamantanes. If resistance to the two drugs were completely independent at 10% apiece, one would expect 1% of the 918 H1N1 isolates, or 9, to be susceptible to both. This suggests there might be a biological reason for the lack of overlap. Stay tuned.

Overall these data confirm what we already knew: this was a much worse flu season than the previous two. The proportion of deaths attributed to pneumonia and influenza peaked in mid-March and was higher than previous years. Here’s a time series going back to 2004 so you can see the extent of the differences (Source: CDC, Morbidity and Mortality Weekly Reports):

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83 of the deaths were in children, spread out over 33 states. The bad vaccine match may have contributed to the severity, although studies one on subpopulations strongly suggest that the vaccine had partial to good effectiveness for influenza A despite the mismatches.

While the pandemic flu shoe didn’t drop this year, influenza still left a pretty big foot print.

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Comments

  1. #1 Greg
    June 30, 2008

    Do you have a reference for the partial effectiveness of the vaccine for A viruses despite being a mismatch? I’d be interested to read it, especially since I’ve been trying to convince family and friends to get the vaccine partially on the basis of that sort of benefit.

  2. #2 revere
    June 30, 2008

    Greg: Summary here, but if you Google (CDC Marshfield Clinic vaccine) you’ll find links. In CDC’s MMWR of April 18, 2008.

  3. #3 anon
    June 30, 2008

    why is there so few flu in Britain since 2000 ?

  4. #4 Dylan
    July 1, 2008

    I suspect that you’re not going to like this, much, Revere: (and neither do I, really); and please forgive the terrible thread drift; but just the same, I’m afraid that we are just about in the same position (collectively), with respect to our knowledge of how exactly influenza functions — in all of its myriad, manifest, mystical ramifications — as we are with respect to the nature of the Higgs boson, in physics; its mediation between the states that we recognize as electromagnetic energy, and that imponderable “thing” that we recognize as “mass.” The Higgs boson is probably — at least in part — the solution to the problem of integrating the in-fractious Quantum Theory, with the so far irreconcilable (and profoundly sophisticated, and elegant, and remarkably beautiful Relativity theories of Einstein). A “troubling, inscrutable, incalculable, entirely theoretical particle;” seemingly parts the waters that separate the vast continents that divide the seemingly irreconcilable space, where the speed of light coalesces into “common matter.” It is the common denominator of “empty space;” as though there ever was such an entity. It is the “mystery,” and the “stuff” of the vacuum. Beyond the bounds of infinity. Perhaps beyond Eternity. Certainly beyond knowing.

    Influenza, I suspect, has its own “Higgs bosons;” we cannot find them, because we simply do not know where, or how, to search for them. Influenza is neither “good,” nor “bad,” as Nature sees it. But it does things. And only our collective hubris comforts us into believing that we know either how, or why, or what, or even when.

    I believe that you are troubled because you perceive what you believe to be a colossal storm on the horizon. You know that many of us share your concern. This “community” has done all that it can, with what it has at its disposal (meager, at best); and we have done it openly, candidly, and in full knowledge of the ridicule that we were likely to be subjected to. We went ahead, anyway. We still plod on. Because we still perceive — clearly — the vast magnitude of the unmitigated danger.

    We are not there, yet; but the sense is, even among the myriad Governments, now, that it is closing in. When communication crumbles, and shuts down, to protect paltry territory, that is never a good sign. And it is cropping up all over. The pandemic (perhaps the one to end all pandemics), does not require our assistance; but it is getting a shit load of it, all the same. I am totally convinced that we deserve much of the credit (such as it is) for arousing, and focusing, many of the otherwise perpetually somnolent, moribund Governments, on the nature and immediacy of this approaching catastrophe

    I will not stop until the “Beast” is dead. It is dreadful, hideous, and powerful beyond belief. I have met it, and it does not surrender meekly. The battle was epic. And nearly cost me my life. And that is what is in our future. And that confrontation is very likely in our most immediate future.

  5. #5 Influenza
    July 1, 2008

    Influenza virus is a deadly lethal weapon which moves on slowly at initial stage but on prolonged time in our body, its causes serious effects. Si i favor for the complete eradication of this influenza virus.