Trivalent influenza vaccine for the 2010-2011 season

10 March 2010

influenza-vaccineThe World Health Organization and the US Food & Drug Administration have decided on the composition of the influenza virus vaccine that will be used during the 2010-2011 season in the northern hemisphere. The trivalent preparation will contain the following influenza virus strains: A/California/7/2009 (H1N1); A/Perth/16/2009 (H3N2); and B/Brisbane/60/2008. The same trivalent vaccine is also being used to prepare for the upcoming winter in the southern hemisphere.

The A/California/7/2009 (H1N1) virus is the pandemic strain that was used in the 2009 H1N1 monovalent vaccine. That virus has not yet undergone sufficient antigenic drift to warrant selection of a new strain for the vaccine. Note that a seasonal H1N1 strain from previous years will not be included in the vaccine. This change has been made because epidemiological evidence suggests that these viruses will probably not circulate at significant levels during the 2010-2011 northern hemisphere season. Although the vast majority of circulating influenza viruses in humans are related to the 2009 H1N1 pandemic strain, sporadic influenza A(H3N2) activity continues to be reported in several countries. This is the reason why an H3N2 component is part of the vaccine.

The selection of viruses for seasonal flu vaccines is based on which influenza viruses circulate during the previous season. Sample viruses are collected by 130 national influenza centers in 101 countries and data on disease trends are analyzed by the four World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza. Vaccine viruses are selected which will most likely protect against the main circulating viruses during the next influenza season. WHO makes recommendations about which specific virus strains should be included in the vaccine. Individual countries then decide which viruses will be included in the influenza vaccine.

Even though the 2009 H1N1 strain has not undergone significant antigenic changes, it’s important to be immunized again in anticipation of the next influenza season. That’s because immunity conferred by the vaccine isn’t particularly long lasting. As Adolfo Garcia-Sastre told me today*, even if influenza didn’t change, you would still have to be immunized every year to protect against infection.

*I recorded our conversation. Look for it at TWiV within the next few weeks.

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  • Pippie00044
    I'm not taking this vaccine , there is no way to know for sure what is actually in these things ???
  • Nicky
    I am a high risk patient and can't find anywhere that has the flu vaccine available. Can anybody please tell me where I can find a clinic or private practice that might still have stock. If I die of this flu virus, can my family sue the government??? Apparently, although I suffer from asthma I was shown the door at a government clinic. They told me to go elsewhere and said they didn't have stock although I know of people that got their vaccines at the same clinic. What is happening to this country???
  • elizevdschyff
    Please help I need 5 vaccines a.s.a.p - South Africa
  • So why is killed-polio vaccine able to give longer lasting immunity than this flu vaccine?
  • Terrific question. A good one for a virology exam! Basically the
    inactivated flu vaccines don't induce immune memory - and why that is
    isn't known. One issue might be the fact that the virions in the
    vaccine are disrupted with detergent, and therefore barely resemble
    infectious virions. Or the absence of internal virion components might
    play a role. The inactivated poliovirus vaccine, on the other hand, is
    not disrupted - the virions are largely intact, and that might
    contribute to inducing robust memory.
  • iayork
    I think that's part of it, but not the whole story. The inactivated flu vaccine does give a memory response, but it's relatively short-lived, a year to a few years. But even the live flu vaccine (the cold-adapted virus) gives a relatively short-lived response as well -- longer than the inactivated version, but not spectacularly so.

    So is it something intrinsic to influenza? (It's not impossible -- for example, noroviruses tend to only induce very short-lived immunity, so this is something that viruses may be able to manipulate a little.) But we do know that anti-flu immunity can last a very long time. Remember the paper a couple years ago that showed immunity in modern survivors of the 1918 flu, 90 years later.

    On the third hand (we need a squid to debate this properly), that's not directly comparable, because they weren't measuring the same thing in that study. They were restimulating first and then looking for the memory. In general, detection of long-lasting memory has taken that approach, because antibody titers decay away fairly quickly (unless there's restimulation in vivo) even when memory cells are present. I don't know of studies where that's been done with the flu vaccines (doesn't mean the studies aren't out there, just that I don't know of them) -- how much memory is left after the antibody titers wanes, and how recoverable is that memory?

    I also don't know how directly comparable the polio studies were -- were they picking up circulating antibody in the absence of restimulation (the flu situation) or restimulating in the process and picking up on the memory response from reactivated memory cells?

    But yeah, the disruption is probably a big part of it. Better innate triggers from the incorporated RNA and probably virion proteins. Probably better CD4 help as well (particulate material, perhaps including virions, is better phagocytosed and presented on MHC class II for T cell help than is soluble protein). Giving a more potent adjuvant with the flu vaccine (the emulsion that's used in Europe) does lead to a longer-lasting response, as I recall.

    The live vaccine for flu is mucosal which tends to have less long-lasting memory in general, though it's not universally true. So I'm guess the short antibody response to the inactivated and the live vaccines are for different reasons.

    I also wonder how much impact pre-existing cross-reactive immunity to other flu strains would have. I'd be surprised if there was no effect at all from our annual exposure to different strains, and I'd guess that would tend to reduce the effective dose of the flu vaccine compared to polio, and might lead to amplification of the "wrong" (cross-reactive but non-neutralizing) response.

    Mostly guesswork, I'm afraid. Sorry for the stream of consciousness rambling.


  • Thanks for those great comments. Your point about the adjuvant is correct: Adolfo mentioned yesterday that adjuvants would probably be useful for a longer-lasting response.
  • I wish I knew more immunology.
    So what is inducing "memory"? We're getting a response... enough Abs to protect, why no memory cells?
    How well has this been tested?
    We always assume we need a new vaccine because of drift.
    Since I've had a few flu shots over the years, I'm not terribly worried if I occasionally miss one (unless different viruses.
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