So Does The Flu Vaccine Work Or Not?

A paper that came out Wednesday on influenza vaccine efficacy has generated a new round of speculation about what is probably the hardest sell in the vaccine business. There’s a lot to complain about with our current flu vaccines: everyone needs a new shot every year, vaccine makers don’t always guess right about which strains of flu will be circulating that season, and plenty of people can tell stories about how they got the shot and still got sick.

Now, in the middle of flu vaccine season, we get a new peer-reviewed report – and of course an accompanying press release – that seems to bring more bad news:

“Evidence for consistent high-level protection is elusive for the present generation of vaccines, especially in individuals at risk of medical complications or those aged 65 years or older. The ongoing health burden caused by seasonal influenza and the potential global effect of a severe pandemic suggests an urgent need for a new generation of more highly effective and cross-protective vaccines that can be manufactured rapidly”, explains Michael Osterholm from the University of Minnesota, USA, lead author of the study.

The news coverage was a mixed bag, ranging from predictable rantings from the antivaccination nuts (no links – you can find them yourself) to balanced, nuanced explanations such as this. Most of it was somewhere in between, no doubt confusing plenty of regular folks.

While Mark Crislip provided a typically excellent and thorough overview of flu vaccine efficacy back in ’09, I’m just going to highlight a few important features of the new paper from Osterholm’s group.

First, there’s not really any news here. Yes, Osterholm and his colleagues did yeoman’s work mining the literature and compiling their data, but they could not escape the fundamental limitations of all meta-analyses. In a meta-analysis, researchers look at existing publications, pick the ones that meet a particular (and in this case extremely strict) set of criteria, and compile the results into a new paper. There’s no new experimentation involved.

Furthermore, the conclusion of this particular meta-analysis should surprise exactly nobody. We’ve known for a long time that flu vaccines are imperfect, and while Osterholm has now put specific numbers on that imperfection for particular age groups, those numbers are neither definitive nor shocking.

Osterholm’s latest results weren’t exactly secret, either. He presented them at the National Influenza Vaccine Summit in May, and the conference report I wrote for them went on the NIVS web site this summer. It may not be in the top of everyone’s news feed, but anyone who’s really tracked this issue closely already knew these results were coming.

These findings don’t alter the main conclusion of decades of public health advice, either. Flu vaccines aren’t 100% effective, but given their outstanding safety record, and the very real risks involved in catching the flu, they’re a whole lot better than nothing.

Finally, while the study’s headline conclusion was that vaccine efficacy averages only around 59% in healthy adults, the team also found that the H1N1 pandemic flu vaccine was a bit above average (69% effective), and discovered even better results for the live attenuated flu vaccine (LAIV, also known as FluMist) in one of the groups at highest risk of severe flu infection:

By contrast, LAIV showed significant protection against infection in young children, preventing influenza in 83% of children aged 7 years or younger. However, the Advisory Committee on Immunization Practices (ACIP) does not currently recommend LAIV over TIV in these children.

Besides its apparently higher efficacy, FluMist has another huge advantage: it’s inhaled rather than injected. My daughter used to scream her head off each Fall before, during, and after her flu shot. Now she can barely stop giggling through the procedure. With the new meta-analysis showing that this snorted vaccine is probably more effective for her than the shot, I can feel good about it as both a virologist and a father.

6 thoughts on “So Does The Flu Vaccine Work Or Not?

  1. Pingback: How good is the influenza vaccine?

  2. Stephen St Jeor

    A point that wasn’t addressed is the high dose flu vaccine (4x more antigen) given to individuals over 65 years old. I understand that gives a stronger immune response. Is there any data to support its efficacy?

  3. Brian Hanley

    It is worth remembering that there are multiple kinds of vaccine efficacy.

    There is sterilizing immunity and priming immunity. Priming immunity, such as would be expected to be conferred on the 40% who may experience an illness, is still valuable to the individual. It significantly shortens the illness and lowers morbidity. For people with asthma and the elderly, that can be lifesaving.

    If a broad, detailed study were done, one would expect to find a fair degree of continuum in viral load in a range. On one end is sterilizing immunity. This would be expected to slide from very minor viral loads, to a disease shorter by one or two days.

    There is evidence that strongly suggests that, for instance, measles vaccine confers this kind of immunity. In outbreaks certain closed groups of vaccinateds probably had circulating infectious carriers who were unaware that they were.

    Titers on vaccinated mothers with measles tend to be low, and this manifests in their infants with an earlier loss of maternal antibody immunity. Newborns typically have titers roughl 1.5 – 1.8 times that of the mother. Half life is around 40 days.

    Very few vaccines are as good as vaccinia is for producing immunity. This makes a difference in how we should be talking and thinking about vaccination and efficacy. Public health decisions are being made based on an overly simplistic model of what vaccine efficacy is.

  4. R.Blake

    I’ve read (through researching the different types of flu vaccine) that the FluMist (inhaled) vaccine is not safe for asthmatics and should not be used by them or certain age groups (which I fail to remember). Anyone recommending it should alert to these caveats.

  5. DCPattie

    I have yet to read the study but in my view the study should have separated flu seasons where the match (vaccine-to-virus) is good and poor. We already know that the vaccine is less effective when there is a poor match (hello, that’s why the vaccine formulation changes yearly). To lump it all together and call it an analysis is shameful.

    1. Alan Post author

      That’s a problem the authors openly acknowledge and account for, but it also highlights the difficulty of doing any type of flu vaccine trial. Clinical trials are extremely expensive, and if you have the bad luck to do one in a year where there’s a mismatch between the vaccine and the predominant strain, you’re left with borderline-useless results and no way to get the money back. The usual workaround is to use antibody titers as a surrogate measure of vaccine efficacy, but in this meta-analysis they looked only at studies that tracked viral loads. The fundamental issue is that there’s no perfect way to ask these questions, so we’re stuck with incomplete answers. This most recent analysis is just feeling another leg of the elephant.

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