2017 flu vaccine effectiveness – getting the facts straight

The upcoming flu season may be a rough one. A strain of the influenza A, H3N2, is showing up in small clusters of outbreaks throughout the USA. Unfortunately, the 2017 flu vaccine effectiveness against the H3N2 may be lower than expected.

We will get into the details further in this post, but I do not want to bury the headline. This does not mean the 2017-18 flu vaccine is ineffective – the quadrivalent 2017 flu vaccine effectiveness against three of four flu strains is still fairly high. The flu vaccine is extremely important in stop lots of flu strains, and just because it may have an issue with one of the four strains, does not imply that it is useless.

Let me repeat that, just in case someone misses the point – only one of the four strains of flu in the 2017-18 vaccine may have lower effectiveness. The vaccine remains highly effective against the other four strains.

Flu complications

Influenza attacks all ages, but the highest rates of complications and mortality are in the elderly, those 65 years old and above, and the young. And if those individuals have a comorbidity such as diabetes, hypertension or cardiovascular disease, the risk of death goes up significantly.

But some strains of the flu, like H1N1, has a tendency to cause significant complications for healthy young adults. The flu attacks everyone.

Worldwide, the flu averages between 250 and 500 thousand annual deaths. The elderly account for 90% of those deaths. According to the CDC, there is a wide variety of complications that arise from upper and lower respiratory tract flu infections. Pneumonia, brain, muscle and heart inflammation, and multiple organ failure are the more serious complications from the flu. Influenza is the leading cause of admission to the hospital from infectious diseases among seniors.

Because of the aforementioned immunosenescence, influenza vaccine effectiveness is often lower in the elderly. Moreover, the elderly have a higher incidence of having a comorbidity that increases the risk of serious complications from the flu.

There are myths that the flu isn’t anything to worry about. That’s simply not true.

Picking antigens for 2017 flu vaccine

I think there is an impression (trope, myth, meme) that scientists throw darts at a dartboard to determine the make up of the flu vaccine. Reality is far from this belief amongst the anti-vaccine religion.

Let’s explain how the vaccine actually works. Without getting too complicated, the flu vaccine induces a systemic immune response to a part of the influenza virus called hemagglutinin, which is a glycoprotein found on the surface of influenza viruses. Both inactivated and live influenza vaccines induce virus-specific serum antibodies which can protect against infection with wild influenza virus possessing the same hemagglutinin antigen.

The reason that each flu season brings a new risk for contracting the disease is that the virus has frequent mutations of the hemagglutinin, so the immune system doesn’t recognize the virus anymore, and you contract the flu. It doesn’t matter if you get the flu “naturally” or boost your immune system with a vaccine, you are generally susceptible to the newly mutated flu virus each year.

Of course, this makes it difficult to develop a flu vaccine every year, because national health organizations, like the US Centers for Disease Control and Prevention, have to scientifically predict which mutated viruses might be prevalent in the upcoming flu season. It’s difficult to predict the exact antigen if there are frequent mutations in the flu virus. In addition, there is evidence that growing the virus in eggs may actually increase the rate of mutations, causing the vaccine to have a different antigen than in the wild flu virus.

Unfortunately, vaccine manufacturers require a six month lead time from choosing the virus to shipping the vaccine, scientists must quickly determine what the new mutated types might be.

The first step is that over 100 national influenza centers in 100 countries receive and test virus samples from patients in their countries. These centers then send samples of the most prevalent viruses to five World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza,  which include the following research organizations:

Twice a year, February for the Northern Hemisphere and September for the Southern Hemisphere, WHO gathers the five Collaborating Centers to meet and discuss which flu virus mutations are going to be prevalent.

The key scientists from each of these centers review the results of surveillance, laboratory, and clinical studies, and the availability of vaccine viruses and make recommendations on the composition of the upcoming season’s influenza vaccine. Generally, the group decides on three subtypes of the flu virus – H1N1 (a subtype of A flu), H3N2 (another subtype of A flu), and type B strains. Recently, a second subtype of the B type virus is included in the quadrivalent flu vaccines.

WHO recommends specific vaccine viruses for inclusion in influenza vaccines; however, each country reviews the data and may modify the viruses in the vaccines for their own country. For example, in the USA, the Food and Drug Administration (FDA) makes the final decision about vaccine viruses, with input from the CDC, that will be used in vaccines sold in the USA.

This is difficult scientific work. It would be much better if we had two or three years to figure out the right flu vaccine each season – but that’s not possible. And we need to stress an important point again – the scientist get it right for most flu strains in most years.

2017 flu vaccine effectives – what we know

In the 2016-17 flu season for the Northern Hemisphere, the CDC estimated that the overall effectiveness of the flu vaccine was around 48%. I realize that’s far from perfect, but given the significant complications and costs of a flu infection, even reducing the risk by half has an important benefit to humans. Furthermore, given the very low risks from getting the shot, the benefit to cost equation is overwhelmingly on the side of benefit.

What we also know is that Australia experienced a difficult flu season (remember their flu season occurs six months prior to the Northern Hemisphere version) with respect to the H3N2 strain of flu. According to the Australian Government Department of Health,

The estimated effectiveness of the 2017 seasonal influenza vaccine was low for influenza A(H3N2), which was the most common virus in circulation throughout the season. The estimated effectiveness for other viruses circulating to a lesser extent was moderate. The reason for this is two-fold. Firstly, the vaccine produces a weaker immune response generally in the elderly. Secondly, this year the influenza A(H3N2) virus seemed to undergo some change during the year and general vaccine protection was less across the whole community for this strain.

The Australian Department of Health estimated (pdf) that the overall effectiveness for the flu vaccine was 33%, but may have been as low as 16% in preventing hospitalizations from the flu. Just so I can hammer the point home, the effectiveness against other flu strains was still quite high, although far from perfect.

A new article published in Euro Surveillance stated that the effectiveness against the H3N2 strain may have been as low as 10%. And since the Northern Hemisphere went with the same H3N2 strain for its vaccines this autumn, the USA, Europe, Canada and other areas may experience the same low effectiveness against that one strain of the flu.

As a result of what was observed in Australia, the World Health Organization along with other health organizations have made changes in recommendations for the antigens included in the 2018 southern hemisphere flu vaccine.

I know, I’ve written this about five times in this article – the effectiveness against other flu strains was still quite high, although far from perfect. And unless you are a fan of the Nirvana fallacy, that is, if it’s not perfect, it’s bad – the flu vaccine is still better than catching the flu.

Flu vaccine effectiveness varies from year to year:

2006 – 2007 52%
2007 – 2008 37%
2008 – 2009 41%
2009 – 2010 56%
2010 – 2011 60%
2011 – 2012 47%
2012 – 2013 49%
2013 – 2014 52%
2014 – 2015 19%
2015 – 2016 48%*
2016 – 2017 42%*

*  Estimated.

These numbers are for all strains, and they are often lowered by relatively low effectiveness against one of the three or four strains in each season’s flu vaccine. This is the issue with the 2017 flu vaccine effectiveness, with the lower benefit in protecting against the H3N2 strain.

It is possible that the observations in Australia may not lead to a similar experience in the northern hemisphere. Maybe the H3N2 strain that became prevalent in Australia does not show up in the USA and other countries. That’s possible.

2017 flu vaccine effectiveness summary

Yes, the flu vaccine for the upcoming 2017-18 might be less effective than we wish. It’s not because of scientific incompetence. It’s not because it’s worthless.

It’s effectiveness may be lower against one of the four strains of flu in the current vaccine – the H3N2 strain. The effectiveness against the other strains of flu, the H1N1 and two influenza B strains, is still fairly high.

In addition, there is plenty of evidence that individuals who contract influenza after vaccination have better outcomes. Even in high risk patients.

Ignore the clickbait headlines, even from respected websites,  that claim that the current flu vaccine is “only 10% effective.” That’s untrue. We don’t know how it effective it might be in the northern hemisphere until an analysis is done in the spring of 2018. Moreover, that’s the effectiveness against one of the four strains of flu.

Get your flu vaccine. Vaccinate your kids against the flu. It’s the best choice for your health.


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The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!