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EM - Seasonal Flu: Why I Got Vaccinated

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  • EM - Seasonal Flu: Why I Got Vaccinated

    Seasonal flu: Why I got vaccinated

    Category: Infectious diseaseInfluenza treatmentSwine fluVaccines
    Posted on: September 17, 2009 6:24 AM, by revere


    I just got my seasonal flu shot. It was free and my medical center is encouraging everyone to get one. I wouldn't be telling the truth if I said I didn't feel it at all, but in all honesty, I hardly felt it. They must be using smaller needles these days. Anyway, given that most circulating flu virus is pandemic swine flu H1N1, for which a vaccine is not yet available (coming soon to a clinic near you, we're told), you might wonder why I -- or anyone --would bother. I'll do my best to explain my reasoning, but I'll grant at the outset I may have missed some good reasons or have reasons that are fallacious -- you decide. The pandemic has produced lots of questions that don't have easy answers. But I've been asked here a number of times what I was going to do and why, so I thought I'd give you an explanation.


    As I'm sure all readers here know by now, the currently available flu vaccine is the usual seasonal trivalent vaccine (three components) designed to protect against circulating flu viruses influenza A/H1N1 (Brisbane), A/H3N2 (Brisbane) and influenza B (Victoria). Since flu virus changes every couple of years in ways that aren't always predictable yet the vaccine has to be produced before we see what strains are actually circulating, there is always the risk of a mismatch -- i.e., the prediction was wrong. That's happened with one or another component of the vaccine a few times in recent years, although it's thought that even mismatched vaccine gives some protection (the unhappy corollary is that even properly matched vaccines often fail to protect a significant fraction of vaccinees from infection; see our post about efficacy here). So how are we doing with matching this year?


    Since the seasonal flu season hasn't gotten underway in earnest (if indeed there will be one with seasonal subtypes), we don't know yet, but the data up through week 35 (beginning of September), which is the most recent, shows the seasonal H1N1 is a complete match, that is, since October 1st of last year (the administrative start of CDC's flu season), all of the seasonal flu A/H1N1 matched the vaccine component for this year, including up to last week. That's a good sign that if seasonal H1N1 starts circulating again in earnest, the vaccination I got will give me maximum protection. In my age group (65+) it's not clear how good that protection is. The immune systems of older folks doesn't respond with the same alacrity as that of younger folks (as in many other things, alas), but if there's seasonal H1N1 around like what we're seeing now I've done the best I can as far as a vaccine goes. The news for the H3N2 and flu B components is not quite as good, although (so far) not terrible. The match over the last year for H3N2 is 93% and for flu B 89%. So these subtypes are changing and if both or either start circulating and change even more the vaccine won't have done as well by me. But it will still have some efficacy -- and potentially quite a bit -- so I judged it netted out positively.
    Let's review for a moment what vaccine efficacy means. Really well matched vaccines can have efficacies of 70% or 80%. What that means is that if you compare the amount of influenza in a vaccinated group to an unvaccinated one, the amount of flu will be 70% (or 80%) less in the vaccinated group. That's not complete protection, but it's pretty good. Let's be sure you understand exactly what this means. For clarity, let's take 50% efficacy. This means that if you are exposed to enough flu virus that would have infected you without vaccination, your chance of actually getting the flu is now like a flip of the coin (50%). That sounds bad until you realize that the people you are being compared with are people who aren't vaccinated and who are playing with a coin that has tails on both sides. I know which coin I'd rather play with.


    But of course there's more to it this year. We are in a very complicated situation, because the vaccine I got is thought to give me no protection against the virus that, at the moment, is the overwhelmingly predominant circulating influenza virus, the pandemic swine flu H1N1. The epidemiology of this virus is quite different from seasonal flu. For one thing it has been infecting people since April, straight through the summer, during a time when seasonal flu is normally at very low levels. Although we haven't been doing surveillance during summer months since we didn't think we had to (because we didn't think there was any flu around), we could have been wrong that there's hardly any flu in the summer. We just weren't looking for it. But this year we have been doing virologic surveillance in the summer and it shows hardly any seasonal flu -- 1 - 2% at most. So there are two possibilities. One is that seasonal flu is behaving as normal, and more or less disappears in the summer (that's why flu is call "seasonal," after all); or that it's been there in other years and we've never looked for it but that this year pandemic swine flu has crowded it out of the host marketplace (however that happens). Either way, almost all the flu A virus that's out there now is pandemic swine flu, the virus for which the vaccine I just got gives me no protection. So why did I get it?


    Below is a graph I showed last week, from CDC's FluView surveillance webpage. It's the product of CDC's Emerging Infections Program (EIP), a population-based surveillance network that monitors trends in laboratory-confirmed influenza-associated hospitalizations. The font is kind of small, so if you want to see the it full screen you can go here. What it is showing you is how the risk of winding up in the hospital with a lab confirmed case of influenza (any type or subtype) is shaping up since April, when the pandemic started. The horizontal dotted line in each panel is the average risk incurred in that age group over the last three flu seasons. Thus if this year is like the average of the last three years, you would expect the risk in your age group to rise to the level of the dotted line by the time the flu season is over. You can see that the risk is quite different this year for different age groups. I'm in the age group in the bottom panel (>65 years old):
    The risk level is expressed on the vertical axis. For example, the number 2.0, the top value in the second panel, means that the risk of winding up in the hospital with a laboratory confirmed case of flu is 2/10,000 or 0.02%. It's important to note that the scales in the top and the bottom panels are different than the four in the middle. Looking at these age groups what you see is the risks have ramped up most quickly in the 5 - 17 year old and 18 - 49 year old age groups, where the risk of hospitalization for lab confirmed flu has already reached or exceeded what it was at the end of the flu season, even though we are now at a time when we haven't even started CDC's official flu season. In the under 4 year old and the 50 to 64 year old groups, we're already half way there, as well. In my age group, we've hardly budged. It looks like a normal seasonal flu picture, with risks just beginning to edge upward as fall is coming on. This confirms data from other surveillance activities that, for reasons that aren't clear, the over 65 age group is being affected dramatically less than normal for flu. For swine flu deaths, my age groups is contributing perhaps 2% of the mortality, whereas for a normal (seasonal) flu season, the over 65 contribute about 90% of the deaths.


    Remember, however, that I mentioned the difference in scales. CDC says (correctly) that the age group at highest risk is the under two year olds. If we look at the risks, we see why:
    Rates for children aged 0-23 months, 2-4 years, and 5-17 years were 2.5, 1.0, and 0.8 per 10,000, respectively. Rates for adults aged 18-49 years, 50-64 years, and >= 65 years, the overall flu rates were 0.5, 0.6, and 0.5 per 10,000, respectively. (CDC FLuView, Influenza-associated hospitalizations)
    What this says is that although the rates for children and adults ramped up much faster than the normal (low) rates, rates for my age group are so high that we are still about even, all somewhere around .5/10,000 people in our respective age groups, or 0.005%. Thus my risk of winding up in the hospital as a lab confirmed flu case is about the same as an adult over the age of 18. The risk for the under 2 year old age group is five times higher (2.5/10.000), which is why CDC says they are at greatest risk.


    What I don't know (and I don't know if CDC knows either) is what is putting the 65+ group into the hospital at this moment. More to the point, I don't know what will put my age group into the hospital as the flu season progresses. Here are the possibilities:


    i. Pandemic swine flu A/H1N1 2009 almost completely replaces both subtypes of seasonal flu (seasonal H1N1 and seasonal H3N2) and there's hardly any of it around. Then I get no or little benefit from getting vaccinated (except for the flu B part, which is significant). Since last week 2% of the isolates were seasonal flu, it's hard to say what will happen. We don't usually see much seasonal flu virus this early in the year anyway. Will the future be different?
    ii. Pandemic flu and seasonal flu co-circulate. We don't know if that can or will happen. But since I'm in the age group that dies from seasonal flu, I've done the right thing.
    iii. Pandemic flu and seasonal flu are out of phase. For example pandemic flu has a sharp but short history and by virtue of using up susceptibles and vaccination it's essentially gone by January, leaving an opening for the seasonal viruses to return and act as they usually do. Again, I've done the right thing.
    iv. Pandemic flu changes character and starts to infect my age group, crowds out seasonal flu or something else. Depending on the nature of the changes (maybe it reassorts with something the vaccine works for) I might or might not have come out ahead and everyone else, of all age groups, might or might not come out ahead if they are vaccinated with the seasonal flu vaccine.
    The truth is this. No one knows what's going to happen. We're all guessing. But in my estimation, the risk-benefit calculation for vaccine side-effects and flu is so markedly in favor of the vaccine that I made the decision to get vaccinated and that's what I'd advise others, too. How confident am I? I'm confident it is the most rational thing to do given what we know. But flu confounds us at every turn, so being confident about anything else in this case is not something I'm confident about.

  • #2
    Re: EM - Seasonal Flu: Why I Got Vaccinated

    I got the seasonal flu shot too.

    Comment


    • #3
      Re: EM - Seasonal Flu: Why I Got Vaccinated

      For what it is worth, I got the seasonal vaccine on the 17th also.
      In addition to all the reasons listed above why someone would get vaccinated for protection, in a healthcare setting the most important reason to get vaccinated is so that I don't infect a patient or someone else with influenza.
      JT
      Thought has a dual purpose in ethics: to affirm life, and to lead from ethical impulses to a rational course of action - Teaching Reverence for Life -Albert Schweitzer. JT

      Comment


      • #4
        Re: EM - Seasonal Flu: Why I Got Vaccinated

        I'm pleased that you tried a probability and damage estimation analysis !
        I had wished you would do the same with birdflu.
        Would you get a birdflu-vax if available ?



        explain the difference between efficacy and effectiveness

        seasonal shot gives ~10% protection against ******* in adults.

        H3N2 kills ~twice as many older people than H1N1,B so when we have both,
        as last season, then then the H1N1-vax may increase your chances to get H3N2.

        How much does the vax reduce your chance to die from flu ?
        Maybe 10^-5, I guess.

        We have the chance to support ****** in crowding out the more deadly H3N2 and maybe
        killing it forever, as happened with H2N2.

        the vax didn't really reduce the seasonal deaths in practice.
        I'm interested in expert panflu damage estimates
        my current links: http://bit.ly/hFI7H ILI-charts: http://bit.ly/CcRgT

        Comment


        • #5
          Re: EM - Seasonal Flu: Why I Got Vaccinated

          efficacy(flu) effectiveness(ILI)
          ------------------------------------------------------------------------
          children>2y.live virus 79% 33%
          children>2y.dead virus 59% 36%
          adults live virus 48% 15%
          adults dead virus 70% 25%


          absenteeism with vaccination is reduced by 0.16 days per year per case
          absenteeism with vaccination is reduced by 0.4 days per year
          6% reduction of clinical cases (ILI)


          South Africa : 3.75 fold return on investment for vaccination due to reduced absenteeism
          10-12% of absenteeism is due to flu

          Amantadine:61%
          Rimantadine:64%
          NI:74%


          5%-15% of people get flu per season
          25% get ILI
          10% of ILI is flu

          36000 die of flu in USA per year




          http://www.blackwell-synergy.com/doi...ournalCode=vhe

          average absenteeism due to ILI is 1.3 days per year = 137$



          http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract

          airline personal showed 40% fewer ILI and 26% fewer absenteeism due to ILI


          $47 saved per vaccinated employer 1995 NJM

          http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract
          ~4days absenteeinsm per I/ILI

          http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract
          ILI halfed on vaccination


          OK, I had been wondering about this ...
          0.4 days absenteeism per year is prevented by vaccination.

          10% of people catch the flu per season, causing
          about 4 days of absenteeism. So 0.4 days would mean
          that the vaccine is 100% efficient.
          Well, apparantly the vaccine is also efficient for non-flu ILI (?)
          (T-cell (cell based) immunity ?) but not so well.
          With 70% efficacy we'd get, that about 0.6 days absenteeism
          per year is due to flu and 0.7 due to non-flu ILI.

          "efficacy was 70%, "efficiency" was 25%, so we'd expect 1.3/3 = 0.325
          days of absenteeism-reduction per year by considering clinical ILI.

          Assuming absenteeism is proprtional to death risk,
          that figure would suggest that in a pandemic
          and vaccine with same efficacy and 20%CAR and 50%CFR
          vaccination would prevent 455million deaths while 195million
          would still die.

          ---------------------------------------------------

          I walked through the recent articles at pubmed/medline
          (2007, some 2006)

          someone else please do the same with 2006,2005 !

          ------------------------

          ILI in vaccinated,non-vaccinated HCWs in Taiwan : 13.6%,15% (367,40)
          cost per saved working day was $36

          1298 elderly Spanish community dwellers with OECD
          one death prevented per 187 vaccinations

          150 to 300 vaccinations in elderly needed to prevent one death in Sweden

          flu-vaccinating cancer-patients in USA costs $224 per quality-adjusted life-years gained

          2003f efficiency in Children against MAARI was 26%
          Efficacy against confirmed influenza was 56%

          0.98 days fewer absenteeism in workers in Saudi-Arabia within 4 months after vaccination
          net saving of $28 per vaccinated worker

          effectiveness in young was 49%. Partially vaccinated children who were aged 6 to 23 months had no significant reduction in influenza, but partially vaccinated children who were aged 24 to 59 months
          had a significant (65%) reduction in influenza,

          efficacy of inactivated vaccine was 77%,75%,67% (3 confirmation methods), in 2004f in Michigan
          efficacies of live attenuated vaccine were 57%, 48%,30%
          The difference in efficacy related to flu-B

          n=423HCWs ,2002f, Italy , vaccination effect:
          ILI : 24% to 15%. days absenteism
          Absenteism-days: 1.22 to 0.74
          Total cost : 135 to 97

          ---------------------------------------------------------------

          ---------------------------------------------------------------------

          Efficacy and effectiveness of influenza vaccines in elderly people: a systematic review.
          Jefferson T,
          Rivetti D,
          Rivetti A,
          Rudin M,
          Di Pietrantonj C,
          Demicheli V.
          Cochrane Vaccines Field, ASL 20, 15100 Alessandria, Italy. Toj1@aol.com

          BACKGROUND: Influenza vaccination of elderly individuals is recommended worldwide. Our aim was to review the evidence of efficacy and effectiveness of influenza vaccines in individuals aged 65 years or older. METHODS: We searched five electronic databases to December, 2004, in any language, for randomised (n=5), cohort (n=49), and case-control (n=10) studies, assessing efficacy against influenza (reduction in laboratory-confirmed cases) or effectiveness against influenza-like illness (reduction in symptomatic cases). We expressed vaccine efficacy or effectiveness as a proportion, using the formula VE=1-relative risk (RR) or VE*=1-odds ratio (OR). We analysed the following outcomes: influenza, influenza-like illness, hospital admissions, complications, and deaths. FINDINGS: In homes for elderly individuals (with good vaccine match and high viral circulation) the effectiveness of vaccines against influenza-like illness was 23% (95% CI 6-36) and non-significant against influenza (RR 1.04, 0.43-2.51). Well matched vaccines prevented pneumonia (VE 46%, 30-58) and hospital admission (VE 45%, 16-64) for and deaths from influenza or pneumonia (VE 42%, 17-59), and reduced all-cause mortality (VE 60%, 23-79). In elderly individuals living in the community, vaccines were not significantly effective against influenza (RR 0.19, 0.02-2.01), influenza-like illness (RR 1.05, 0.58-1.89), or pneumonia (RR 0.88, 0.64-1.20). Well matched vaccines prevented hospital admission for influenza and pneumonia (VE 26%, 12-38) and all-cause mortality (VE 42%, 24-55). After adjustment for confounders, vaccine performance was improved for admissions to hospital for influenza or pneumonia (VE* 27%, 21-33), respiratory diseases (VE* 22%, 15-28), and cardiac disease (VE* 24%, 18-30), and for all-cause mortality (VE* 47%, 39-54). INTERPRETATION: In long-term care facilities, where vaccination is most effective against complications, the aims of the vaccination campaign are fulfilled, at least in part. However, according to reliable evidence the usefulness of vaccines in the community is modest.
          _________________
          I'm interested in expert panflu damage estimates
          my current links: http://bit.ly/hFI7H ILI-charts: http://bit.ly/CcRgT

          Comment


          • #6
            Re: EM - Seasonal Flu: Why I Got Vaccinated

            I appreciate an altruistic spirit in health care providers, as long as their actions regarding vaccine acceptance are voluntary. I don't want any group to have less human rights or value than any other group.

            Catching the flu, though, is bottom on my list for reasons to avoid hospitalization as far as iatrogenic risks.

            http://emedicine.medscape.com/article/967022-overview
            Hospital-Acquired Infections

            Author: Quoc V Nguyen, MD, Assistant Professor, Department of Pediatrics, New York State Health Department
            Contributor Information and Disclosures

            Updated: Jan 14, 2009

            Background

            Hospital-acquired infections (HAIs), also known as health-care–associated infections, encompass almost all clinically evident infections that do not originate from a patient's original admitting diagnosis. Within hours after admission, a patient's flora begins to acquire characteristics of the surrounding bacterial pool. Most infections that become clinically evident after 48 hours of hospitalization are considered hospital-acquired. Infections that occur after the patient's discharge from the hospital can be considered to have a nosocomial origin if the organisms were acquired during the hospital stay.
            Pathophysiology

            Within hours of admission, colonies of hospital strains of bacteria develop in the patient's skin, respiratory tract, and genitourinary tract. Risks factors for the invasion of colonizing pathogens can be categorized into 3 areas: iatrogenic, organizational, and patient-related.

            * Iatrogenic risk factors include pathogens on the hands of medical personnel, invasive procedures (eg, intubation and extended ventilation, indwelling vascular lines, urine catheterization), and antibiotic use and prophylaxis.
            * Organizational risk factors include contaminated air-conditioning systems, contaminated water systems, and staffing and physical layout of the facility (eg, nurse-to-patient ratio, open beds close together).
            * Patient risk factors include the severity of illness, underlying immunocompromised state, and length of stay....
            Never forget Excalibur.
            “‘i love myself.’ the quietest. simplest. most powerful. revolution ever.” ---- nayyirah waheed
            Avatar: Franz Marc, Liegender Hund im Schnee 1911 (My posts are not intended as advice or professional assessments of any kind.)

            Comment


            • #7
              Re: EM - Seasonal Flu: Why I Got Vaccinated

              wait until we see, whether seasonal flu (and which) is coming to your area

              then you can still get vaccinated. It's also more effective when given shortly
              before the outbreak (2weeks)


              vaccinate the superspreaders (school-children, traveling salesmen,...)
              I'm interested in expert panflu damage estimates
              my current links: http://bit.ly/hFI7H ILI-charts: http://bit.ly/CcRgT

              Comment


              • #8
                Re: EM - Seasonal Flu: Why I Got Vaccinated

                My 19 year old son also received the seasonal flu shot.

                We did it for the following reasons:

                1) We have tolerated past flu shots very well. No side affects at all.
                2) We do not like getting sick.
                3) We would like to know if we become ill with influenza which strain it might be (without lengthy testing).
                4) We are both very social and see many people. We do not want to spread any illness we have to others.
                5) We do not want to overburden our health care workers by getting sick. I have a chronic pre-existing condition. My son has a cytokine storm type of reaction with any illness he gets - a very high fever and total recovery in a day or two.
                6) Possible - and very remote - chance of a cross immunity effect for other strains of influenza. What if a seasonal influenza shot can just take the edge off a pandemic strain? Probably not. But for my adult children - it gives me peace of mind that I have done everything I can for them.


                Would I take a vaccination against bird flu? Probably. I would like to have more facts before I decide.

                I am 100% against forced vaccination. It is a personal choice.

                Comment

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