# Flu vaccine question **URL:** \ **Category:** Factual Questions\ **Created:** [January 18, 2015, 6:58pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194 "2015-01-18T18:58:18Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![wolfman](https://avatars.discourse-cdn.com/v4/letter/w/a8b319/32.png) [@wolfman](https://boards.straightdope.com/u/wolfman)\ **Post date:** [January 18, 2015, 6:58pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/1 "2015-01-18T18:58:18Z")
Something I have wondered about, but can’t find anything that addresses it. So they put three or four common strains of the virus in each year’s batch based on prevalent strains and best guess. It’s pretty widely reported now that the prediction wasn’t very good this year, and the virus mutated into versions that the vaccine didn’t prepare immune systems for very well. The thing I haven’t seen covered is how much good previous year’s vaccine does. In this specific case and in general. If person A has been getting the flu vaccine every year for ten years, and person B got their first ever shot this year, does A have a measurable advantage in avoiding the flu that given year? Do the common flu viruses mutate so fast and so completely that no antibodies more than 12 months old are any good, or do you start to build up a spectrum of flu immunities over the years that help you. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [January 18, 2015, 7:11pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/2 "2015-01-18T19:11:34Z")
Good question ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [January 18, 2015, 7:28pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/3 "2015-01-18T19:28:42Z")
I think there are two separate questions here: (1) As you get varying flu shots every year, “do you start to build up a spectrum of flu immunities over the years” (OP’s wording) that covers a bunch of different strains that you might encounter in the future? Or is each year’s new strain SO different that prior years’ vaccines don’t count? But also: (2) How long do those various immunities persist anyway? On this, ISTM I’ve seen it mentioned in some article somewhere: Not very long. Unlike some other immunities that are long-lasting (e.g., the tetanus shot that needs a boosted every 10 years; or the Sabin polio vaccine that was supposedly life-long), the impression was that the annual flu immunity fades relatively quickly. To whatever extent that is true (if at all?), I gather that your past history if flu shots doesn’t help you much in the long run. ETA: Okay, now that I’ve spouted off with some vague uncited recollection, I’m starting to do some actual googling: how long does flu immunity last. My immediate result is: Lots of hits. I’ll come back when I’ve found something particularly helpful-looking. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [January 18, 2015, 7:40pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/4 "2015-01-18T19:40:38Z")
Okay, here’s one cite: Article in TIME Magazine, Aug. 26, 2008, discussing one researcher’s findings that looked at still-living survivors of the 1918 flu epidemic, and found that their antibodies to that flu are still strong. [http://content.time.com/time/health/article/0,8599,1835907,00.html](http://content.time.com/time/health/article/0,8599,1835907,00.html) ETA: As I’m skimming through the various top hits from that google search, one thing I’m noticing (not too surprisingly) is that most of the discussions DON’T distinguish much between the two separate questions. Most of the seem to ask the question “Does the flu vaccine last very long?” but then focus more on answering the other questions instead, that the doesn’t work well from year-to-year because of the changing strains. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [January 18, 2015, 7:51pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/5 "2015-01-18T19:51:23Z")
As I’m skimming some cites, I’m seeing a common pattern showing up: A lot of them are saying something to the effect: The flu vaccine immunity is long-lasting, where “long-lasting” seems to be defined as “one year, long enough to get you through one flu season”. Uh, thanks. That’s not the kind of long-lasting, y’know, _long-lasting_ that the OP (and I) are probably looking for. Example: [When Should You Get A Flu Vaccine (Flu Shot), And How Long Does It Last?](http://abcnews.go.com/Health/ColdandFluQuestions/story?id=5677892), James Conway M.D. on ABC News, Sept. 25, 2008: > [@](#): > > The immunity from the vaccine actually lasts for a substantial period of time. In past years people used to be concerned that the immunity would fade but we have much better data now that supports that immunity actually can extend throughout the influenza season into the spring, and in many cases actually into the following year. Still, we want everybody to get influenza vaccine each and every year since the vaccine is slightly different from year to year and you want maximal protection for that upcoming flu season as quickly as possible and as early as possible. Okay, it’s “long-lasting”. For certain values of “long-lasting”. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [January 18, 2015, 10:12pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/6 "2015-01-18T22:12:39Z")
They are actually very difficult questions to answer because it really depends on who is being vaccinated and with what and how protected is being defined. The elderly for example have less strong of responses to the vaccines and it fades faster. The live weakened nasal vaccine has in the past provided more protection from antigenic drift (we’ll se how it did this year) and should theoretically produce more lasting immunity as it induces both the antibody response (easy to measure) and the longer lasting but harder measure cellular immune response. And natural disease produces some longer lasting protection to the particular strain for the same reason. The injectable only does the antibody side of the protection spectrum (which again, fades faster, _probably_ by a year). The nasal though works better in kids than in adults (although it still works in adults fine enough) precisely because kids are less likely to already be immune. The virus needs to replicate in the nasal mucosa some to induce the response and being immune already may reduce how well it can do that. Still it does seem [to work](http://onlinelibrary.wiley.com/doi/10.1111/j.1750-2659.2009.00124.x/abstract) year on year in kids so go figure. To summarize: 1. The injectable flu vaccine probably does not help one build up a spectrum of antibodies. The antibody levels probably fade to below protective levels by a year or two out and on the early side for the elderly. Not so much because the virus changes each year but a drifted one won’t be much protected all by previous years’ shots. 2. Not sure well the antibody type protection (humoral) for influenza seems to fade so relatively quickly. Again the nasal vaccine’s induction of some cellular protective response should be longer lasting but I don’t know how long it has been followed out. ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [January 18, 2015, 10:36pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/7 "2015-01-18T22:36:52Z")
I really wouldn’t have a personal problem with multiple flu vaccinations every year if it would have any effect on preventing or reducing the severity of flu. I’d seek it out. The downside to a flu vaccination is a slight needle prick, a much smaller needle than 40 years ago, a sore arm and a slow day or two. It is, overall, a very safe vaccination and the more people who get them, the number of people suffering is vastly reduced. ---
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [January 19, 2015, 1:03am UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/8 "2015-01-19T01:03:34Z")
Wasn’t this year’s vaccine (2014-2015) exactly the same as last year’s vaccine (2013-2014)? I thought that’s why it was available in August this year, instead of October; they had a head start making it. That would support the notion that they don’t expect the immunity to last beyond a year, as we weren’t told we could skip it this year if we got it last year. (Or the notion that the CDC really are evil bastards raking money in hand over fist by giving out bad medical advice, but as that’s an antivax position, I’m disinclined to believe it.) ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [January 19, 2015, 1:43am UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/9 "2015-01-19T01:43:38Z")
I think the fact is that no one really knows how much protection with the injectable lasts from season to season. The reason **Senegoid** ’s link was talking long lasting as lasting through out the season was the belief that some held for a long time that if one (especially an older one) got vaccinated “too soon” in the season it might be warn off with a flu peak in later January or February. That turns out to be clearly not the case. Trying to find information on protection lasting _between_ seasons is not so easy … I did find [this](http://jid.oxfordjournals.org/content/210/1/126.abstract) though, published a year ago. > [@](#): > > We estimate vaccine effectiveness (VE) against both influenza A/subtypes and B/lineages in Canada for the 2011–2012 trivalent inactivated influenza vaccine (TIV) with components entirely unchanged from the 2010–2011 TIV and in the context of phenotypic and genotypic characterization of circulating viruses. … Summarizing what they found was that the next season vaccine efficacy was at 80% for one component (pandemic H1N1 A); 51% for H3N2 A and for B. 80% is pretty good but 51% is not generally considered good enough. And digging a bit more also [this](http://cid.oxfordjournals.org/content/59/10/1375.full) published just a few months ago that directly addresses the op: > [@](#): > > **Impact of Repeated Vaccination on Vaccine Effectiveness Against Influenza A(H3N2) and B During 8 Seasons** … > > … With our longitudinal influenza vaccination records, we were able to examine the independent and combined effectiveness of current-season vaccination and prior vaccination history over multiple seasons. Current-season vaccination was effective against medically attended H3N2 and B virus–associated illness regardless of prior vaccination history. > > The observed protection among persons vaccinated during the previous season and not the current season suggests that influenza vaccines received \>1 year earlier may provide some residual protection. A case-control study of influenza VE in pregnant women during the 2010–2011 and 2011–2012 seasons found patterns similar to our study with evidence of residual protection from previous-season vaccination [10]. VE results from the 2010–2011 season in Canada were also consistent with residual protection against A(H1N1)pdm09 among individuals who were previously vaccinated with an adjuvanted monovalent vaccine [9]. In our cohort, residual protection against H3N2 viruses occurred despite the fact that the predominant H3N2 viruses were antigenically distinct from the previous season H3N2 vaccine component in 5 of 7 seasons that were included in the H3N2 analysis. Similarly, the predominant circulating B lineage differed from the previous season vaccine lineage in 5 of 7 seasons, and both lineages circulated widely in 1 season (2012–2013). This residual protection may be conferred by immune responses elicited by previous vaccines that cross-react with current-season virus antigens. … > > … In conclusion, we found that vaccination provided protection against medically attended influenza infection, regardless of prior vaccination history. This is consistent with randomized clinical trials of influenza vaccine efficacy [38]. However, this study raises relevant questions about the potential interference of repeated annual influenza vaccination and possible residual protection from previous season vaccination that have not been considered in most trials. Further observational studies that include simultaneous assessment of immune response, both to vaccine antigens and previously circulating viruses, and clinical protection would be helpful. Such is the current state of the art. Still fuzzy and of course more research is needed. As always. FWIW. ---
**Author:** ![wolfman](https://avatars.discourse-cdn.com/v4/letter/w/a8b319/32.png) [@wolfman](https://boards.straightdope.com/u/wolfman)\ **Post date:** [January 9, 2018, 12:54am UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/10 "2018-01-09T00:54:23Z")
Since it’s GQ I’m waking up my thread since I came across some relevant study, in case anybody else was still interested. > **[Adults who get flu shots every year are better protected](https://www.nbcnews.com/health/health-news/here-s-another-reason-get-flu-shots-every-year-n835901)** > > Here’s a reason to get a flu shot every year: people who got a new shot every flu season were less likely to die or end up in the hospital with severe flu. Looks like a study was recently done that shows repeated vaccinations is providing greater flu immunity and resistance to severe symptoms. It’s just a national news report so details are a big non-speciifc but it sounds like a broader spectrum _is_ creating by the body’s immune system > [@](#): > > And repeated vaccination may cause broader immunity, both Topham and the researchers said. Vaccines stimulate both the production of antibodies and cells called T-cells to fight germs. Repeated vaccination might more effectively boost the action of T-cells. ETA, at least for over 65ers which was the only population in the study. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [January 9, 2018, 7:11am UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/11 "2018-01-09T07:11:09Z")
Well, I’m convinced. I’m going to get my flu shot every Tuesday this year! ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [January 9, 2018, 1:51pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/12 "2018-01-09T13:51:23Z")
A reminder that while preliminary reports suggested this year’s flu vaccine was only “10%” effective, that apparently was based on reports from Australia. A recent update suggests Americans [can expect better effectiveness](https://whyy.org/articles/vaccine-years-flu-effective-portrayed-cdc-says/). Still waiting for the holy grail of a “universal” flu vaccine. ---
**Author:** ![Noel\_Prosequi](https://avatars.discourse-cdn.com/v4/letter/n/b19c9b/32.png) [@Noel\_Prosequi](https://boards.straightdope.com/u/Noel_Prosequi)\ **Post date:** [January 10, 2018, 2:22am UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/13 "2018-01-10T02:22:04Z")
Humph. In the southern winter in Australia, we had the worst flu season in decades. I was vaccinated. And got the flu. In America. (Cue Fred Flintstone grumble-swearing.) Still, get the vaccine. I gather Australia’s problem was a misjudgment about what to include in the vax.) ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [January 10, 2018, 2:33am UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/14 "2018-01-10T02:33:27Z")
> [@Jackmannii](#): > > A reminder that while preliminary reports suggested this year’s flu vaccine was only “10%” effective, that apparently was based on reports from Australia. > > A recent update suggests Americans [can expect better effectiveness](https://whyy.org/articles/vaccine-years-flu-effective-portrayed-cdc-says/). > > Still waiting for the holy grail of a “universal” flu vaccine. That article’s main point is that the “10%” refers to efficacy against H3N2 but in Australia when “it came to overall effectiveness against any of the multiple strains of flu, the vaccine worked about 30 percent of the time.” The other bit though is that the Australian program offers the flu vaccine for free through the National Program [_only_ to those at high risk](https://www.nytimes.com/2017/09/19/world/australia/flu-vaccination-deaths.html?_r=0) (the elderly, those with at risk medical conditions, etc.), populations that typically have poorer responses to the vaccine than the younger and healthier, and have poor rates with the rest of the population, that responds better. > [@](#): > > … The numbers are not flattering: under 10 percent of children get flu vaccinations, said the National Center for Immunization Research and Surveillance. The figure for children in the United States is nearly four times higher. … There’s an Australian selection bias for those most likely to respond poorly. The best way to protect the high risk individuals is for the rest of us, especially the spewing fountains of germs that are otherwise healthy children, immunized as completely as possible, and thereby to minimize exposure of those at higher risk. As to the original question of the op, [this from Lancet](http://www.thelancet.com/pdfs/journals/lanres/PIIS2213-2600(17)30475-7.pdf). > [@](#): > > … Some studies suggest that flu vaccine effectiveness might be higher in people receiving the influenza vaccine for the first time compared with people who have been vaccinated more than once; the data from the Australian influenza season estimated reduced effectiveness in those who had received the vaccine in 2016. Other studies, however, have found no evidence that repeat vaccination results in someone having less protection. … Putting that together with the already referenced study which showed that repeated vaccination is very effective compared to single season at preventing more serious to fatal compared to less serious cases … it seems the answer is complicated. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [January 10, 2018, 1:07pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/15 "2018-01-10T13:07:06Z")
> [@DSeid](#): > > That article’s main point is that the “10%” refers to efficacy against H3N2 but in Australia when “it came to overall effectiveness against any of the multiple strains of flu, the vaccine worked about 30 percent of the time.” It’s been reported that Australia’s selection of flu viruses is not the same as ours; therefore preliminary estimates of how well the vaccine would work in the U.S. were too gloomy. \*"…a recent report in the journal F1000 Research found the Australian strain of H3N2 is not identical to the predominant virus circulating in the United States. “The majority of the viruses are well-covered by the vaccine,” said lead researcher Dr. Slobodan Paessler, a professor in the department of pathology at the University of Texas Medical Branch in Galveston. “There are some minor groups of viruses that are not well-covered,” he added." “The current vaccine in the U.S., in contrast to the Australian [vaccine], will work because we have most of the American H3N2 viruses, rather than the Australian one,” Paessler explained."\* > **[What Is the Flu?](https://www.webmd.com/cold-and-flu/what-is-flu)** > > Learn more from WebMD about the flu, including causes, symptoms, types, risk factors, treatment, and prevention. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [January 10, 2018, 3:09pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/16 "2018-01-10T15:09:15Z")
> [@DSeid](#): > > There’s an Australian selection bias for those most likely to respond poorly. It is an interesting question. However, I would note that although the government subsidised free flu-vax is only for the at risk groups, the vaccination is very easy to get, and very cheap. Many companies provide it to employees for free, and you can get vaccinated at many pharmacies for the princely sum of $20 (15 USD.) Usually no harder than walk up, pay, roll up your sleeve. Vaccination rates for the flu in general seem to be of the order of 85%. The at risk groups seems to actually pull the average down, with only about 70% update. The flu vaccination last year became a little controversial as many more died than usual, although not as bad as 2009. It came to the point where the government senior medical officer was denying that they had purchased sub-standard cheap vaccinations. Where it seems some of the numbers became skewed was indeed that the predominant strain circulating (H3N2) was the one that causes more problems in the elderly. But there was an element of general dissatisfaction last year. But last year was an anomaly. You would not want to base general views on efficacy on 2017 in Oz. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [January 10, 2018, 10:58pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/17 "2018-01-10T22:58:36Z")
So far, the effectiveness of the 2017-2018 flu vaccine in the US & Europe seems to be better than anticipated from the early results from Australia. But the flu season is just beginning to hit its peak here now. Australia isn’t always a good predictor, for a couple of reasons: 1. the ‘origin’ of new flu strains is in Southeast Asia, quite close to Australia (and with lots of human travel between them). So the flu strains in Australia can be newer ones, mutated from the ones that were chosen last March/April to put in the vaccine. So the vaccine seems to be more effective here, where we are likely fighting off some of the older strains of the flu. 2. Australia seems to have a lower vaccination rate – mostly given to those seen as at risk. Here, it seems to be pushed for everybody. Especially children, who are often the vector for spreading flu. So the basic ‘herd immunity’ effect applies. (I’ve also seen some questions about the Australian statistics. They are based only on patients who are sick enough to go to the doctor, not including patients who have mild cases or don’t get flu at all. I don’t know enough about statistics & disease to judge this, but personally, when I’ve had a case of flu, I didn’t bother going to the doctor – I knew what he’d say: “drink plenty of fluids, take aspirin, etc, for pain, and rest in bed”.) ---
**Author:** ![constanze](https://avatars.discourse-cdn.com/v4/letter/c/f9ae1b/32.png) [@constanze](https://boards.straightdope.com/u/constanze)\ **Post date:** [January 11, 2018, 9:25am UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/18 "2018-01-11T09:25:44Z")
> [@Senegoid](#): > > (2) How long do those various immunities persist anyway? On this, ISTM I’ve seen it mentioned in some article somewhere: Not very long. Unlike some other immunities that are long-lasting (e.g., the tetanus shot that needs a boosted every 10 years; or the Sabin polio vaccine that was supposedly life-long), the impression was that the annual flu immunity fades relatively quickly. That does raise an interesting related question: how / why does the human body’s immunesystem decide to Keep antibodies around at all, and for how Long? On the one Hand, the human Body in General takes as many energy saving measures as possible: muscles that aren’t used regularly are built back; bones that aren’t stressed regularly get thinner; the brain falls into repetitive Patterns as often as possible - so why do some antibodies stick around for life? On the other Hand, Polio, measles, Tetanus are potentially deadly, so keeping antibodies against them forever would be a better choice. So how does the immune System figure out “Those antibodies are important, Keep them” and “Those are less important, let’s Forget them to save Memory space”? ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [January 11, 2018, 1:38pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/19 "2018-01-11T13:38:53Z")
As a _general_ rule, very general, your body will keep up immunity for about 10 years after a vaccination if you have no further exposure to the pathogen in that time. This is a reason for getting a tetanus/diphtheria/pertussis booster every ten years - most people _aren’t_ exposed to those, so immunity fades with time. Now, it used to be that something like a measles vaccination would be “for life” because the average person _would_ be exposed to the disease from time to time, acting as a sort of natural booster. Now that we have beaten back such disease so thoroughly we’re finding adults are loosing their immunities due to lack of re-exposure. So… basically, if your body doesn’t re-encounter something within 10 years it will tend to drop the immunity. If it does re-encounter it (you don’t have to be sick, just exposed) it will maintain the immunity. Very roughly - I’m sure that there are all sorts of conflating factors involved. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [January 11, 2018, 5:17pm UTC](https://boards.straightdope.com/t/flu-vaccine-question/710194/20 "2018-01-11T17:17:37Z")
The conflating factors though are where it gets so fun! The kicker in this is that immunity persistence is most easily measured (and inferred) by antibody levels but lasting functional immune protection is often provided without significant antibody levels by T cells that have persistent “memory” of the germ … which are not so easily measured. And how well those memory T cells develop may be impacted by age at exposure with early exposure potentially resulting in T cell memory protection that may be lifelong. So to bring this to the i[nfluenza discussion](https://www.frontiersin.org/articles/10.3389/fimmu.2012.00357/full) at hand … > [@](#): > > … Memory T cells provide protection against re-infection with the same pathogen enabling a more rapid recovery of the host and a milder clinical outcome (Powell et al., 2007). For example, survival from the H2N2 influenza pandemic of 1957 was attributed to pre-existing T cell immunity in the adult population (Epstein, 2006). Furthermore, high levels of pre-existing CD4+ T cell memory correlate with reduced viral loads and clinical scores in a human influenza challenge study, highlighting the importance of T cell memory in viral infection (Wilkinson et al., 2012). Once established, memory T cells can reside in tissues or recirculate between the blood, organs, and lymph nodes. … > > … Our recent antigenic analysis of the 2009-H1N1 virus, showed that this newly emerged pandemic virus shared immunogenic peptides with the catastrophic 1918-H1N1 strain (Gras et al., 2010), and shared antigenic similarity with viruses present prior to 1945. This resulted in the detection of cross-reactive CD8+ T cell immunity between the H1N1-2009-infected donors and 1918 derived peptides for the NP418 epitope restricted by the large HLA-B7+ family. Cross-reactive immunity between the pandemic 2009-H1N1 strain and the 1918-H1N1 strain (as well as other H1N1 viruses from the beginning of the century) at both T cell and antibody levels may have resulted in lower susceptibility to the H1N1-2009 in individuals \>65 years of age, with the majority of severe cases occurring in young adults (the mean patient age was 24 years; Cao et al., 2009; Agrati et al., 2010). This was in contrast to the usual scenario of the elderly population being more susceptible to annual, seasonal epidemics caused by influenza A viruses (Couch et al., 1986; Webster, 2000). Therefore, the lack of T cell immunity in younger adults and children, and the persistence of cross-reactive memory T cells in older individuals may partially account for the demographics of infection. The question thus still remains whether memory CD8+ T cell populations to influenza strains encountered early in life persist for a life-time. … That universal “holy grail” will almost certainly be one most effective given young and aimed at a memory T cell response. [Next page](https://boards.straightdope.com/t/flu-vaccine-question/710194.md?page=2)