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Is the flu vaccine only 12% effective?


  • The flu vaccine has low effectiveness, but that effectiveness is still better than nothing
  • It has higher effectiveness in some age groups, lower in others
  • There was a mismatch between the most common H3N2 influenza strain and the vaccine, bringing the effectiveness lower
  • We need better influenza vaccine technology… Like, now!

Of Sacred Cows And Such

I’ve told you before that I don’t believe in sacred cows when it comes to science. Yes, even vaccines are subject to criticism when they don’t work or when the benefits are not really there. Antivaxxers who attack me sometimes will say that I “worship” vaccines. I don’t. When the evidence is there that vaccines don’t work, they I support looking for a better alternative. I didn’t freak out when an old rotavirus vaccine was removed from the market because it increased the chances of children having intussusception.

So news comes today that the flu vaccine for this season has not been very effective in preventing influenza disease in the people who took it. This is from the CDC’s Morbidity and Mortality Weekly Report:

“This report presents an initial estimate of seasonal influenza vaccine effectiveness at preventing laboratory-confirmed influenza virus infection associated with medically attended ARI [acute respiratory illness] based on data from 2,321 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network (Flu VE) during November 10, 2014–January 2, 2015. During this period, overall vaccine effectiveness (VE) (adjusted for study site, age, sex, race/ethnicity, self-rated health, and days from illness onset to enrollment) against laboratory-confirmed influenza associated with medically attended ARI was 23% (95% confidence interval [CI] = 8%–36%).”

The first thing you need to note is that this is effectiveness overall, meaning effectiveness for all people enrolled in the network. That percentage is actually pretty low, but it is still better than nothing. If you were falling from a plane, and I gave you a choice between a parachute that only opens about 1 in 4 times and another that never opened, which one would you choose? You’d choose the one that has a 1 in 4 chance, right?

“If it’s not 100% safe and 100% effective, it’s 100% Satan’s blood”

The problem with humans is that we often fall into the nirvana fallacy, where something that isn’t perfect is not good enough. It is often the first thing that antivaxxers will say about all vaccines. In a big outbreak of disease, you’re always going to have a few who are fully immunized against the disease. This is because nothing in the known universe is 100% effective. But they will use this as justification for saying, “See! The vaccine doesn’t work!”

Likewise, they’re already starting to say that the flu vaccine doesn’t work because it’s only 23% effective. Then they emphasize that the vaccine is even less effective in certain age groups. From the same MMWR report:

“The adjusted VE for all ages against medically attended ARI caused by influenza A (H3N2) virus infection was 22% (CI = 5%–35%). The adjusted, age-stratified VE point estimates were 26% for persons aged 6 months–17 years, 12% for persons aged 18–49 years, and 14% for persons aged ≥50 years (Table 2).”

Again, when looking at these data and deciding whether or not you want to get the flu vaccine, you have to ask yourself if you want 0% effectiveness in not vaccinating, or the levels indicated above if you do vaccinate. If you think that not vaccinating is better, then I have a bridge to sell you.

So why is the effectiveness so low? Again, from the report:

“Overall, the estimate suggests that the 2014–15 influenza vaccine has low effectiveness against circulating influenza A (H3N2) viruses. These early findings are consistent with laboratory data demonstrating that most influenza A (H3N2) viruses circulating in the community are antigenically and genetically different from A/Texas/50/2012, the A (H3N2) component of the 2014–15 Northern Hemisphere influenza vaccine. The predominant A (H3N2) viruses detected through surveillance during the 2014–15 season have been similar to the A/Switzerland/9715293/2013 (H3N2) virus, the H3N2 virus selected for the 2015 Southern Hemisphere influenza vaccine (2).”

It’s just like I told you a few weeks back, the mismatch in viruses is going to throw a lot of people for a loop. With most cases being the Switzerland strain of H3N2, and with the vaccine not providing coverage for that strain, it stands to reason that effectiveness would be low. This is not surprising to me. This doesn’t mean that the vaccine doesn’t work. It means that the vaccine was not a good match for the strain. That plus the fact that we need a better vaccine gives us these low numbers.

So, is the flu vaccine only 12% effective this season? Yes, if you’re in the 18-49 age group. If you’re younger, you have a better shot — no pun intended. Either way, the shot is better than no shot.

One last thing

From the same MMWR report:

“These early VE estimates underscore the need for additional influenza prevention and treatment measures, especially among persons aged ≥65 years, young children, and other persons at higher risk for serious influenza associated complications.§ Influenza antiviral medications should be used as recommended¶ for treatment in patients, regardless of their vaccination status. Antiviral treatment can reduce the duration of illness and reduce complications associated with influenza (4). Antiviral treatment should be used for any patient with suspected or confirmed influenza who is hospitalized, has severe or progressive illness, or is at high risk for complications from influenza, even if the illness seems mild. Persons at high risk include young children (especially children aged <2 years), pregnant women, persons with chronic medical conditions like asthma, diabetes, or heart disease, and adults aged ≥65 years.”

Note that no where in there is there a recommendation that you should demand antiviral medication from your doctor just because you have a soccer game to take the kids to, or a class to attend, or can’t miss work because you can’t afford it… Contrary to what pharmaceutical companies want you to think through their commercials. Ask for antivirals only if you are at risk for serious complications, and take it only if your healthcare provider prescribes it. On top of the flu mutating very fast (sometimes faster than we can make a vaccine against it), we don’t need it getting resistance.

Thank you for your time… And wash your hands.

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René F. Najera, DrPH

I'm a Doctor of Public Health, having studied at the Johns Hopkins University Bloomberg School of Public Health.
All opinions are my own and in no way represent anyone else or any of the organizations for which I work.
About History of Vaccines: I am the editor of the History of Vaccines site, a project of the College of Physicians of Philadelphia. Please read the About page on the site for more information.
About Epidemiological: I am the sole contributor to Epidemiological, my personal blog to discuss all sorts of issues. It also has an About page you should check out.

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