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I recently saw this video featuring Robert Scott Bell, where he basically says that the flu shot is not terribly effective.

Under the video is this description, in part:

Reports in 2013 state that flu shots were only 9% effective for the elderly.

9% sounds dismal. Is that actually the case? Do the reports show that in early 2013 the flu shot was only 9% effective in the elderly?

  • related http://skeptics.stackexchange.com/q/278/6876 – Ryathal Apr 10 '13 at 17:40
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    9% sounds darn good in some comparisons? ["Vaccine effectiveness estimate %, Age ≥ 65 years: ***−32.9%***"](https://www.eurosurveillance.org/content/10.2807/1560-7917.ES2015.20.5.21024?crawler=true&mimetype=application/pdf) A cynic would say that shot formula *was* terribly effective. Although… – LangLаngС Nov 22 '20 at 17:43

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Is that actually the case? : Maybe

Do the reports show that in early 2013 the flu shot was only 9% effective in the elderly? : No

It might be the case that the flu shot's effectiveness was only 9% in the elderly, but the analysis that the CDC does isn't able to support a statement as strong as "the flu shot's effectiveness in group X is Y%". They can only give ranges.

What is true is that the CDC's point estimate for the flu vaccine effectiveness against the 2013 flu A (H3N2) in people aged 65 or older is 9%, with a 95% confidence interval that spans from -84% to 55%. They suggest interpreting these results with caution.

In more general terms, the CDC says the following things:

CDC's vaccine effectiveness study measured lower vaccine effectiveness among people 65 and older against flu A this season than it did among other age groups.

[...]

One possible explanation for this is that some older people did not mount an effective immune response to the flu A (H3N2) component of this season’s vaccine; however, it’s not possible to say this for certain.

Against flu B, effectiveness in the 65 and older age group was found to be similar to that in other age groups: 67% with a 95% confidence interval that spans from 51% to 78%.

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    I'm sorry, but what? If the shot is given to 1000 people how many are effectively protected? If it's 9% then I would think 90 people are protected. –  Apr 10 '13 at 18:44
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    The CDC's measure of vaccine effectiveness represents the reduction in risk provided by the flu vaccine: http://www.cdc.gov/flu/about/qa/vaccineeffect.htm#present-data –  Apr 10 '13 at 18:51
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    How many people are protected is a more complicated question, and would require analyzing the hampered spread of a disease through a partially vaccinated population vs a completely unvaccinated population. For example, even if the vaccine was 100% effective, and given to 400 people in a 1000 person population, that would give some protection to the entire population because the virus can't easily be passed on through those 400 vaccinated people. –  Apr 10 '13 at 19:01
  • What does it mean for the confidence interval to include negative values? How does one interpret a statement like that? – Joshua Frank Nov 15 '18 at 14:00
  • @JoshuaFrank presumably negative effectiveness would indicate that it increased flu cases. In any case the confidence interval is so wide I wouldn't draw conclusions from this – user253751 Apr 19 '21 at 09:56
  • @user253751 you can draw the conclusion that it’s basically a useless vaccine. – froimovi May 21 '21 at 05:55
  • @froimovi It could be 55% effective. There's a 5% probability it's greater than 55%. The study is not powerful enough. – user253751 May 21 '21 at 09:54