There is significant noise claiming that flu shots are largely ineffective, especially against new strains of the flu (see, for example, this site). Both the arguments for, and against, flu shots, claim significant backing from existing research.
How reliable is the information? Are flu shots really effective enough to be worth the cost?
Mark Crislip from the Science Based Medicine Blog has written a very nice overview of various aspects of flu vaccine effectiveness.
First, every year they have to make an educated guess which influenza strains will be circulating 9 months in the future. The better the guess, the better the protection the vaccine should provide. Some years they choose better than others. But often the match between the vaccine and the disease is not optimal, so vaccine efficacy can be decreased. The vaccine works best when there is a good antigentic match between the vaccine and circulating strain of influenza.
The flu vaccine is only effective for the specific strains of influenca it was targeted at. Those strains are adjusted every year, but creating the vaccines takes time, and sometimes an unexpected strain like the swine flu appears and the regular flu vaccines is not adapted to it.
Second, response to the vaccine is not 100%. The older and more immunoincompetent are the least likely to develop a good antibody response to the vaccine. In a bit of medical irony, the more likely a patient is to need protection from the vaccine, the less likely they are to get a protective antibody response from the vaccine.
No vaccine is perfect, but they don't have to work 100% of the time to save some lives.
If the vaccine is worth it is a more difficult question. If you're not one of the risk groups the benefit for you might be relatively small. But as Mark Crislip notes
In my mind that is the true benefit of the influenza vaccines: decreasing the morbidity and mortality of populations. The benefit for populations is derived through vaccinating individuals. That requires a bit of altruism on the part of those receiving the vaccine, as they may be getting vaccinated more for the benefit of others than for themselves.
If you're young and healthy you might not benefit that much, but your grandmother or your child cousin and anyone from a risk group you get in contact with is probably grateful if you vaccinate.
Your point that both sides claim to be backed by scientific studies is also adressed
Do flu vaccines work? It depends on what the meaning of is is. If you are simplistic and like binary answers, yes or no, then you can pick yes or pick no, and find studies to support your contention that the vaccine doesn’t work.
Mark Crislips conclusion is
Or you can look at the preponderance of data, with all the flaws, nuance, subtleties and qualifiers, and conclude the flu vaccine is of benefit. The vaccine decreases the probability of morbidity and mortality. It is a good thing.
which I can only fully agree with. It might not work 100% of the time and not in 100% of the people, but the flu vaccine saves lives and that is enough.
Yes. Influenza vaccines do work but might not be as effective as they could be (or as advertised).
These two reviews should cover the whats, whys and WTFs...
Vaccines for preventing influenza in healthy adults. Cochrane Database of Systematic Reviews 2010, Issue 7. Art. No.: CD001269.
Authors’ conclusions Influenza vaccines have a modest effect in reducing influenza symptoms and working days lost. There is no evidence that they affect complications, such as pneumonia, or transmission.
WARNING: This review includes 15 out of 36 trials funded by industry (four had no funding declaration). An earlier systematic review of 274 influenza vaccine studies published up to 2007 found industry funded studies were published in more prestigious journals and cited more than other studies independently from methodological quality and size. Studies funded from public sources were significantly less likely to report conclusions favorable to the vaccines. The review showed that reliable evidence on influenza vaccines is thin but there is evidence of widespread manipulation of conclusions and spurious notoriety of the studies. The content and conclusions of this review should be interpreted in light of this finding.
Plain Languange Summary
Vaccines to prevent influenza in healthy adults.
Over 200 viruses cause influenza and influenza-like illness which produce the same symptoms (fever, headache, aches and pains, cough and runny noses). Without laboratory tests, doctors cannot tell the two illnesses apart. Both last for days and rarely lead to death or serious illness. At best, vaccines might be effective against only influenza A and B, which represent about 10% of all circulating viruses. Each year, the World Health Organization recommends which viral strains should be included in vaccinations for the forthcoming season. Authors of this review assessed all trials that compared vaccinated people with unvaccinated people. The combined results of these trials showed that under ideal conditions (vaccine completely matching circulating viral configuration) 33 healthy adults need to be vaccinated to avoid one set of influenza symptoms. In average conditions (partially matching vaccine) 100 people need to be vaccinated to avoid one set of influenza symptoms. Vaccine use did not affect the number of people hospitalised or working days lost but caused one case of Guillian-Barré syndrome (a major neurological condition leading to paralysis) for every one million vaccinations. Fifteen of the 36 trials were funded by vaccine companies and four had no funding declaration. Our results may be an optimistic estimate because company-sponsored influenza vaccines trials tend to produce results favorable to their products and some of the evidence comes from trials carried out in ideal viral circulation and matching conditions and because the harms evidence base is limited.
Findings, interpretation and some numbers from Osterholm et al (2012), Efficacy and effectiveness of influenza vaccines: a systematic review and meta-analysis, The Lancet Infectious Diseases, Volume 12, Issue 1, January 2012...
Findings
We screened 5707 articles and identified 31 eligible studies (17 randomised controlled trials and 14 observational studies). Efficacy of TIV was shown in eight (67%) of the 12 seasons analysed in ten randomised controlled trials (pooled efficacy 59% [95% CI 51–67] in adults aged 18–65 years). No such trials met inclusion criteria for children aged 2–17 years or adults aged 65 years or older. Efficacy of LAIV was shown in nine (75%) of the 12 seasons analysed in ten randomised controlled trials (pooled efficacy 83% [69–91]) in children aged 6 months to 7 years. No such trials met inclusion criteria for children aged 8–17 years. Vaccine effectiveness was variable for seasonal influenza: six (35%) of 17 analyses in nine studies showed significant protection against medically attended influenza in the outpatient or inpatient setting. Median monovalent pandemic H1N1 vaccine effectiveness in five observational studies was 69% (range 60–93).Interpretation
Influenza vaccines can provide moderate protection against virologically confirmed influenza, but such protection is greatly reduced or absent in some seasons. Evidence for protection in adults aged 65 years or older is lacking. LAIVs consistently show highest efficacy in young children (aged 6 months to 7 years). New vaccines with improved clinical efficacy and effectiveness are needed to further reduce influenza-related morbidity and mortality.
Vaccine efficacy (95% CI), n = Patients randomly allocated to receive TIV and placebo.
Adults (18–64 years)
75% (42 to 90), n = 728. Healthy adults aged 18–46 years (2004–05) Type A: drifted H3N2; type B: mixed lineage. Ohmit et al (2006)
16% (–171 to 70), n = 1205. Healthy adults aged 18–48 years (2005–06) Type A: drifted H3N2; type B: lineage mismatch (1 isolate). Ohmit et al (2008)
22% (–49 to 59), n = 6203. Healthy adults aged 18–64 years (2005–06) Type A: similar H3N2 and H1N1; type B: lineage mismatch. Beran et al (2009)
62% (46 to 73), n = 7652. Healthy adults aged 18–64 years (2006–07) Type A: similar H3N2; type B: lineage mismatch. Beran et al (2009)
68% (46 to 81), n = 1139. Healthy adults aged 18–49 years (2007–08) Type A: drifted H3N2; type B: lineage mismatch. Monto et al (2009)
50%† (14 to 71), n = 3514. Healthy adults aged 18–49 years (2005–06) Type A: similar H3N2; type B: lineage mismatch. Jackson et al (2010)
50%† (–3 to 75), n = 4144. Healthy adults aged 18–49 years (2006–07) Type A: similar H3N2; type B: mixed lineage. Jackson et al (2010)
63% (one-sided 97·5% lower limit of 47%), n = 7576. Healthy adults aged 18–49 years (2007–08) Type A: mixed strains; type B: lineage mismatch. Frey et al (2010)
76% (9 to 96), n = 506. Adults aged 18–55 years with HIV infection (2008–09) Type A: drifted H1N1; type B: not reported. Madhi et al (2011)
Children (6–24 months)
66% (34 to 82), n = 411. Healthy children aged 6–24 months (1999–2000) Type A: similar H3N2 and H1N1; type B: not reported. Hoberman et al (2003)
–7% (–247 to 67), n = 375. Healthy children aged 6–24 months (2000–01) Type A: similar H3N2 and H1N1; type B: lineage match. Hoberman et al (2003)
Notes
No studies were available for adults aged 65 years or older or children aged 2–17 years.
§ One other study by Loeb and colleagues23 met inclusion criteria and contained data for all age groups.
† Our calculation.
Vaccine efficacy (95% CI), n = Patients randomly allocated to receive LAIV and placebo.
Adults (>=60 years)
Adults (18–49 years)
48% (-7 to 74), n = 725. Healthy adults aged 18–46 years (2004–05). Type A: drifted H3N2; type B: mixed lineage. Ohmit et al (2006)
8% (–194 to 67), n = 1191. Healthy adults aged 18–48 years (2005–06). Type A: drifted H3N2; type B: lineage mismatch (1 isolate). Ohmit et al (2008)
36% (0 to 59), n = 1138. Healthy adults aged 18–49 years (2007–08). Type A: drifted H3N2; type B: lineage mismatch. Monto et al (2009)†
Children (6 months–7 years)
93% (88 to 96), n = 1602. Healthy children aged 15–71 months (1996–97). Type A: similar H3N2; type B: lineage match. Belshe et al (1998)
87% (78 to 93), n = 1358. Healthy children aged 26–85 months (1997–98). Type A: drifted H3N2; type B: not reported (1 isolate). Belshe et al (2000)
84% (74 to 90), n = 1784. Healthy children aged 26–85 months (1997–98). Type A: similar H3N2 and H1N1; type B: lineage match. Vesikari et al (2006)
85% (78 to 90), n = 1119. Healthy children aged 6–<36 months attending day care (2001–02). Type A: similar H3N2 and H1N1; type B: mixed lineage. Vesikari et al (2006)
72% (62 to 80), n = 1886. Healthy children aged 6–<36 months (2000–01). Majority of strains were similar (not reported by type). Bracco Neto et al (2009)
68% (59 to 75), n = 3174. Healthy children aged 12–<36 months (2000–01). Type A: similar H3N2 and H1N1; type B: lineage match. Tam et al (2007)
57% (30 to 74), n = 2947. Healthy children aged 12-<36 months (2001–02). Type A: similar H3N2 and H1N1; type B: mixed lineage. Tam et al (2007)
64% (40 to 79), n = 1233. Healthy children aged 11–<24 months (2002–03). Type A: similar H1N1 and mixed H3N2; type B: mixed lineage. Lum et al (2010)
Notes
No studies were available for adults aged 50–59 years or children aged 8–17 years.
† Authors reported culture, RT-PCR, and RT-PCR/culture; we report RT-PCR/culture results.
Vaccine efficacy (95% CI), n = Patients randomly allocated Vaccine effectiveness against medically attended influenza.
All patients aged 6–59 months admitted to hospital, seen in emergency department or by primary-care doctors for acute respiratory illness (2003–05). Eisenberg et al (2008)
All patients aged 6–59 months admitted to hospital, seen in emergency department (inpatient) or by primary-care doctors (outpatient) for acute respiratory illness (2003–05). Szilagyi et al (2008)
Residents recommended for vaccination by ACIP with acute respiratory illness. Belongia et al (2009)
All patients aged >=9 years presenting with ILI to sentinel primary-care practitioners. Skowronski et al (2009)
Cohort of patients aged 6–35 months presenting with ILI enrolled in a randomised controlled trial for antivirals (2007–08). Heinonen et al
All patients >=65 years old presenting with ILI (2008–09). Savulescu et al (2010)
All patients >=65 years old presenting with ILI (2008–09). Kissling et al (2009)
All patients aged 6–59 months presenting with ILI (2008). Kelly et al (2011)
Adults aged > 50 years admitted to hospital with respiratory symptoms or non-localising fever (2006–09). Talbot et al (2011)
Notes
ACIP = Advisory Committee on Immunization Practices.
ILI = influenza-like illness.
§ Controls tested negative for influenza but positive for other respiratory viruses.
† Vaccine effectiveness against hospitalisation.
The more restrictive selection criteria for study inclusion used by Osterholm and colleagues led to some differences in results from the most recent Cochrane review. The new meta-analysis estimated a pooled inactivated vaccine efficacy against influenza infection in adults of 59% (95% CI 51–67), compared with estimated efficacy in healthy adults of 73% (54–84) in the Cochrane review for years when circulating and vaccine strains were well-matched and 44% (23–59) in years when they were not.
The median vaccine effectiveness of the monovalent pandemic vaccine against medically attended pH1N1 influenza was 69%, whereas in another study effectiveness was estimated to be 90% (95% CI 48–100) against hospital admission due to laboratory-confirmed pH1N1 infection. However, other studies have reported lower vaccine effectiveness for the same outcome. In Australia in 2010, when pH1N1 influenza made up 79% of documented infections, vaccine effectiveness against hospital admission was 49% (13–70). A study undertaken in the Navarra region of Spain in 2010–11 estimated vaccine effectiveness against hospital admission to be 58% (16–79) with a cohort analysis and 59% (4–83) with a test-negative design (J Castilla, Public Health Institute Navarra, Spain; personal communication).
...snip...
Now might also be an appropriate time to use revised estimates of the most probable effectiveness of influenza vaccines to re-examine the effectiveness and cost-effectiveness of some policy options. This re-examination would need to be done in conjunction with studies that, similar to the new meta-analysis of the effect of influenza vaccines, use highly specific laboratory-confirmed outcomes to assess influenza burden.
- source: Estimating the effect of influenza vaccines, The Lancet Infectious Diseases, Volume 12, Issue 1, January 2012.
Most importantly: Always discuss healthcare issues with your doctor...not the internet.
From the CDC website.
Why do estimates of influenza vaccine effectiveness vary widely?
Estimates of influenza vaccine effectiveness are affected by several factors, including the specific study biases discussed above, the match between the vaccine influenza strains and the circulating strains, host factors and the sample size of a specific study. As noted above, the specificity of the outcome measured in a study has an important influence on the observed effectiveness. As more data are collected globally from annual studies that estimate effectiveness for RT-PCR confirmed influenza, it is expected that our estimates will become more refined. However, vaccine effectiveness will always vary from season to season, based upon the degree of similarity between the viruses in the vaccine and those in circulation, as well as other factors. In years when the vaccine strains are not well-matched to circulating strains, vaccine effectiveness is generally lower. In addition, host factors also affect vaccine effectiveness. In general, influenza vaccines are less effective among people with chronic medical conditions and among people age 65 and older, as compared to healthy young adults and older children.
Adults 65 years or older
Only one large randomized, controlled trial of influenza vaccine has been conducted among an elderly population. During the 1991-1992 influenza season, a group of Dutch people 60 years of age and older not living in long-term care facilities (e.g., nursing homes) was studied (Govaert et al., 1994). In this study, vaccine efficacy was 58% in preventing clinically-defined influenza with serologic confirmation of infection. There are no published studies of the efficacy or effectiveness of influenza vaccines in preventing laboratory-confirmed, serious outcomes of influenza such as hospitalization, primarily because the size of the study would be large, and therefore, such a study is very expensive to conduct. Published observational studies conducted among people 65 and older not living in long-term care facilities have used non-specific outcomes, such as pneumonia hospitalizations or all-cause mortality. These studies may be subject to substantial confounding and selection bias, and they use outcomes in which the proportion of illness associated with influenza virus infections vary by season (as other respiratory viruses can cocirculate). As a result, it is difficult to interpret the results of these studies.
Adults 65 years or older in long-term care facilities
All residents of long-term care facilities s (e.g., nursing homes) should receive annual influenza vaccination, as outbreaks of influenza can be explosive and result in substantial morbidity and mortality among residents of such facilities. There is evidence that vaccination prevents respiratory illnesses during periods of influenza circulation for elderly nursing home residents. For example, one study conducted during the 1991-1992 influenza season found that vaccination was associated with a 34% reduction in total respiratory illnesses and a 55% reduction in pneumonia during the two-week peak of influenza activity (Monto, 2001). In addition, one study conducted in UK nursing homes found that vaccinating health care workers decreased deaths during periods of influenza activity during one season with substantial influenza circulation, but not during the next year, when influenza activity was low throughout the winter (Hayward, 2006).
Children
In a four-year randomized, placebo-controlled study of inactivated and live influenza vaccines among children aged 1–15 years, vaccine efficacy was estimated at 77% against influenza A (H3N2) and 91% against influenza A (H1N1) virus infection (Neuzil et al., 2001). A two-year study of children aged 6–24 months found that the vaccine was 66% effective in preventing laboratory-confirmed influenza in one year of the study (Hoberman et al., 2003). Only children who were fully vaccinated (i.e., had either two doses if not previously vaccinated, or one dose if previously vaccinated) versus unvaccinated children were included in the analysis. In the other year of this study, few cases of influenza occurred, making it difficult to assess the vaccine's efficacy (Hoberman et al., 2003). Children younger than 9 years of age who have not been vaccinated previously are recommended to receive two doses of vaccine the first year they get vaccinated. In subsequent years, they need only one dose. This recommendation was made because many children younger than 9 years of age have not been infected with influenza viruses previously, and a booster dose is needed for them to produce a protective immune response.
emphasis mine in all cases
There are plenty more studies on the website but this answer is long enough already, but all studies I looked at showed vaccines were effective, though some where by fairly small margins.
